Balancing S38 ITBs

[macsm5]

Dean, love the sticker. I'm a little way away from being ready to undertake this. Critical to the balancing procedure is correctly adjusted valves, which is a bit of a black art since most of us are going somewhere between .012 and .014 depending on which shims give the closest gap to spec. I suppose that's one of the things that balancing addresses. In addition, setting up the butterflies and linkage mechanism is another important step before attempting to balance the bypass ports. Any plans to add this equipment to the kit/instructions? I can host a .pdf file for you if you want to include it in the thread.

Finally, I would recommend ordering parts number 14 (o-rings) and 16 (blue caps) ahead of time. Compromised o-rings can invalidate the adjustments.

Hi Dean,

In your instructions re: mechanically synchronizing the throttles, you mention to replace the o-ring in the main idle adjuster, in the RealOEM diagram AHAB posted is the main idle adjuster part number 33 and the main idle adjuster "o" ring to replace number 34?

Thanks!

[macsm5]

Dean, love the sticker. I'm a little way away from being ready to undertake this. Critical to the balancing procedure is correctly adjusted valves, which is a bit of a black art since most of us are going somewhere between .012 and .014 depending on which shims give the closest gap to spec. I suppose that's one of the things that balancing addresses. In addition, setting up the butterflies and linkage mechanism is another important step before attempting to balance the bypass ports. Any plans to add this equipment to the kit/instructions? I can host a .pdf file for you if you want to include it in the thread.

Finally, I would recommend ordering parts number 14 (o-rings) and 16 (blue caps) ahead of time. Compromised o-rings can invalidate the adjustments.

Hi Dean,

In your instructions re: mechanically synchronizing the throttles, you mention to replace the o-ring in the main idle adjuster, in the RealOEM diagram AHAB posted is the main idle adjuster part number 33 and the main idle adjuster "o" ring to replace number 34?

Thanks!

[HealeyBN7]

Michael,

Yes. That is correct. The main idle adjustment is the big screw or part number 33 and the o-ring is 34 (11631271346). For some reason, BMW Real OEM didn't list the size of this o-ring as they have for others, but you may be able to match it if you have access to an assortment.

Good luck and let us know how it goes!

Dean

[HealeyBN7]

Mantis whereabouts...

Currently it is on loan to Michael (macsm5) - NoCal - Expected return May 4-5.

Brad (bdalessio) is next on the list - NoCal

Then Eric (ronin) - Spartanburg, South Carolina

Once it is back in SoCal after Eric, perhaps we can schedule in the local sessions.

Sound fair?

Let me know if I missed anyone.

Dean

[HealeyBN7]

Well....I wasn't planning on making another Mantis, but this copy is going to Brad. Thank you Brad!



It has a few improvements:

This version uses nylon barbs on a larger 7 vs 6 port manifold. The larger manifold eliminates 90 degree fittings. The nylon barbs provide a better seal to the vinyl tubing and eliminate the wire ties. I also added thicker (by 1mm OD) high temperature silicone hose to the ends of the vacuum tubes. I think this is a necessary improvement to ensure the business end doesn't deform from heat.

There is also a machined aluminum barb fitting on the large hose. I had to make this one in the lathe as I could not find a 3/16 to 3/8 reducer barb.





It was a good exercise to see how much it cost to make and how much time it takes - too much of both.

Brad should get his Mantis by the end of the week. Eric - I guess you will be next in for the rental as soon as Michael and Brad are finished.

Dean

[ronin]

If you are talking to me, Eric, then just let me know. If you meant a different Eric, that is ok, just let me know where I fit in the schedule. The new and improved version sounds nice. Looking forward to it.

Take care,

Eric

[HealeyBN7]

FYI - The Manometer Kit It is on the road again for a quick loan to David as MinneapM635 in Minneapolis. Should be back and available in a couple weeks.

By the way, shipping seems to have gone up to $20 with insurance. sorry.

Dean

[Das_Prachtstrasse]

What an incredibly fantastic thread. This information is invaluable and will prove to be a cornerstone of mine once this ITB'd M30 is off the ground. Dean, I would be very much appreciative if you would allow me to replicate your design for my own uses as despite my eagerness, international shipping on a borrowed part is folly. Failing that, if you could perhaps be swayed into manufacturing another that would be even more excellent as I'll be needing this tool in due time, and it would be highly useful to those local S38 owners in the click. You'd have to be sure to install the ruler upside down, though.

[HealeyBN7]

I may have a wait until I retire to make another one, but in the mean time feel free to knock off a copy for you and your friends down under. I am thinking that you should be able to figure out all the bits by looking at the pictures. If you need something special let me know. When I put together the second kit for Brad I was shocked how quickly the parts totaled to more then a couple hundred dollars. You of course could save some money of you reused your personal fuel pressure gauge and dial indicator, but be aware that buying the fittings in small quantities is just not frugal.

It is a fun weekend project - get to it!

Dean

[MinneapM635]

Got the Mantis on Monday and immediately plugged it in to get a baseline of where I was at. Last time I synched the throttles was probably 2013 and I used a single mechanical gauge and with all the pulsing, and pinching of the lines, it probably wasn't the best. Here's a video of the readings without any adjustment. Warning, I am a novice at taking and posting videos online... AND keeping my garage tidy.

https://youtu.be/KXkaAa2kSFo

A few quick adjustments and the result:

https://youtu.be/hnNzKgXWEpI

This was without any of the prerequisite "remove the screws, replace o-rings, bottom out and turn out 1 turn" baseline adjustment. So, I set off to do just that last night and wouldn't you know, the o-ring on the idle speed adjustment screw basically disintegrated upon removal of the screw. So, replacement rings ordered on fast shipment. I hope to have the Mantis back in the mail by Monday/Tuesday next week.

Dean, I give credit to you for the tool in the description of the videos. Let me know if you would like me to remove or add any other information. Want to make sure you get the appropriate credit for this great tool.

Thanks,
Dave

[HealeyBN7]

Thanks for the feedback Dave. Looks like you mastered it in short order and the results look great.

It doesn't fix all S38 problems (TPS actuation, ICV response, worn linkage or misalignments, valve clearances, etc), but if the basics are already covered, after tuning, the car should idle a bit more smoothly and if need be you can replace the rotten o-rings or any of the worn ITB components and re-tune to return to a stable flow.

Nice job on the videos! Thanks for linking them to the forum.

Dean

[alim_h]

Hey Dean,

Fairly new to this board and the S38 world. Got the valves adjusted, new cap, new TPS, etc. Still idles rough and down on power. On to throttle syncing. Still loaning out the Mantimanometer? Would love to use it!

Also, when adjusting the butterfly closing gap, does the .01 refer to .01 in or .01 mm? I'm hoping inches otherwise the dial gauge i have doesn't read that fine!

Thanks!

[milarsky]

Hello Alim!

So sorry we never got to meet in Santa Fe, but I will be back next summer.

Have you checked all the following baseline items:

-Coolant Temp Sensor
-Correct Spark plugs (gapped properly)
-Crankshaft/RPM sensor
-Fuel Pressure Regulator
-Oxygen Sensor
-Check for any vacuum leaks?


all best,
Jeff

[alim_h]

Hey Jeff,

Next summer for sure!

Replaced Coolant Temp Sensor, Spark Plugs, and O2 sensor. Checked Crankshaft and Camshaft sensors, as well as FPR. I think I got most of the vacuum leaks. I can read 8 - 9 inHg of vacuum from the EGR port, so I think I should be ok there.

Comes down to AFM and/or throttle bodies now. Actually, I wish I could've swapped AFM's with you to see if that was the culprit. I will probably just do the MAF conversion now, though. I've only heard great things about it.

[HealeyBN7]

Hey Dean,

Fairly new to this board and the S38 world. Got the valves adjusted, new cap, new TPS, etc. Still idles rough and down on power. On to throttle syncing. Still loaning out the Mantimanometer? Would love to use it!

Also, when adjusting the butterfly closing gap, does the .01 refer to .01 in or .01 mm? I'm hoping inches otherwise the dial gauge i have doesn't read that fine!

Thanks!

I would be happy to lend it to you. The gap is measured in inches.

Since you say that you are down on power, In don't think balancing the ITBs will make much difference. It could help with idle smoothness and transition off idle issues, but once the butterfies are partially cracked the bypass screws are no longer in play and any performance issues would come from somewhere else.

Before you balance the ITBs you should make sure your valves are properly adjusted. If you plan on doing that later it will impact the ITB adjustments.

Let me know when you want it sent over. We will need to exchange emails off line so you can paypal me for shipping and a small deposit. Also, if you don't need the dial indicator, all the better. Turns out it is now the only one I have:)

Dean

[Nanajoth]

Since you say that you are down on power, In don't think balancing the ITBs will make much difference. It could help with idle smoothness and transition off idle issues, but once the butterfies are partially cracked the bypass screws are no longer in play and any performance issues would come from somewhere else.



Dean

I reset the OBC MPG tracker before heading out to work this morning. 80 mile round trip. Mostly 80 MPH freeway on the way into work. Traffic on the way home. I haven't see this average before, except in the wife's '84 528e.

Now that's a measurable improvement even on crappy California summer gas blend.

Dean

So what you are saying is that this was due to a difference in your driving style and not your throttle adjustment, sounds misleading.

[HealeyBN7]

Since you say that you are down on power, In don't think balancing the ITBs will make much difference. It could help with idle smoothness and transition off idle issues, but once the butterfies are partially cracked the bypass screws are no longer in play and any performance issues would come from somewhere else.



Dean

I reset the OBC MPG tracker before heading out to work this morning. 80 mile round trip. Mostly 80 MPH freeway on the way into work. Traffic on the way home. I haven't see this average before, except in the wife's '84 528e.

Now that's a measurable improvement even on crappy California summer gas blend.

Dean

So what you are saying is that this was due to a difference in your driving style and not your throttle adjustment, sounds misleading.

You are kidding, right? You took two sentences from this thread separated by seven months and re-ordered them, one as a self report, and the other in response to helping a fellow M5 owner that has an AFM issue and you drew the conclusion that I am trying to be misleading???

If there is something amiss about the process, method or tools described for balancing the ITBs please do share.

Dean

[Nanajoth]

I am curious as to how you gained the extra MPG when you stated that adjusting the ITBs will not help you as far as performance goes and the bypass screws are no longer involved. It looks misleading when you state in the beginning of the thread that you gained all sorts of mileage and compare it to a 528e, then down the road say that this process will not help with performance issues. There is nothing wrong with your adjustment process.

[HealeyBN7]

I am curious as to how you gained the extra MPG when you stated that adjusting the ITBs will not help you as far as performance goes and the bypass screws are no longer involved. It looks misleading when you state in the beginning of the thread that you gained all sorts of mileage and compare it to a 528e, then down the road say that this process will not help with performance issues. There is nothing wrong with your adjustment process.

I think the problem is confusion by the term "performance". I equate performance with power, torque and acceleration, not on idle or off idle efficiency/mileage. See if this helps.

On my M5 the ITBs were fairly far out of adjustment (both the butterflies and the bypass screws). The car struggled (surged) at very low freeway speeds and the ECU/LM2 indicated that it was hunting (...wasting gas). Returning the ITBs to their proper synchronization allowed for much smoother light throttle drive-ability and the resulting "OBC" mileage under ideal conditions. Unfortunately, I don't drive that way most of the time, but you could. If you have an S38 and use the right pedal then you know they are capable of returning you to the filling station in quick order. My mileage has been averaging 18.5-19.5.

The purpose of this thread was not to improve S38 mileage. That was just an observation to demonstrate that the ITBs are no longer "fighting" with each other. I was looking for a repeatable way to adjust the ITBs for on idle smoothness and help with an off idle transition step. The book method of moving the vacuum gauge from port to port was not returning repeatable results.

Regarding Alim's car, he is describing "performance issues" across the power band. Adjusting the ITBs at idle or just off idle really won't have any impact at all at full or part throttle. In off line discussions with Alim it sounds like he may have a bad AFM. I offered to loan him my spare AFM for testing. I recommended that he find the root cause of the "low on power" issue first before investing the in the time to fine tune the ITBs.

Dean

[Nanajoth]

That makes sense, thank you for clarifying.

[wjtesquire]

Wow! Dean was kind enough to share the Mantis Magic Manometer with me and look at the results:

Before:

https://www.youtube.com/watch?v=x91Dia4 ... load_owner

After 5 minutes of adjusting:

https://www.youtube.com/watch?v=nINNnME ... load_owner

I can't tell you how much smoother and more refined my car is running now. I will report back with the MPG data as soon as I can verify it. I highly recommend every S38/M88 owner use this tool. Huge improvements in idle and acceleration.

[wkohler]

Wow. That sounds smoother too!

[tn535i]

My car will sound a bit like the first video if the idle is too low (700 ish) and more like the second at a slightly higher idle (900 ish). I wonder if the idle speed also came up before and after. The S38 is supposed to idle a little higher than most think it should based on other motors. But the balance (or lack of) is really apparent and much improved. I've done mine differently (2 at a time, many measurements/adjustments) but I'm due for a valve adjust and balance and I need to get set up like this.

Good stuff.

[wjtesquire]

I had my idle set higher so it would not struggle when the ac compressor cycled on. With the compressor off, I would see the idle speeds of about 900 rpm. When the a/c compressor cycled on the RPM would dip to about 700. After sync I set the idle to 700 and it doesn't change when the a/c compressor cycles on.

[tn535i]

That is really smooth then for 700 rpm. Nice. But I think BMW would say the idle speed on the S38 should be closer to 800-900 range. It also sounds like it is not dithering but the clip is only a few seconds. Did you look at the O2 output to see if it dithers from rich to lean every few seconds? If not you are supposed to adjust the AFM air bypass until it can dither.

[wjtesquire]

I just calculated my fuel consumption over the last two tankfuls after using the manometer and averaged 16.6 miles per gallon. That is up from 14.3!

[Bhart]

Would a motorcycle synchronizing tool like the http://www.motionpro.com/product/08-0411 do a similar job as the MantisManometer?

[HealeyBN7]

Would a motorcycle synchronizing tool like the http://www.motionpro.com/product/08-0411 do a similar job as the MantisManometer?

Yes, but you need six ports. Not many six cylinder bikes out there:)

Dean

[tn535i]

I've done it with just two port manifold. Almost like using a vacuum gauge but you balance 5 to one master cylinder that you pick, #1 for example. You might have to go through a couple times but you can certainly get it quite good. You'll want some sort of restrictor to take the bounce out and you must be sure to clamp off any tube you remove or the fluid may get sucked out. ATF is good to use because it's easy to see, low viscosity, and if you suck it into the engine it shouldn't hurt anything.

The six port manifold is probably much better.

[Randomg]

Made my first attempt with the mantis this evening. Boy were my cylinders off. I was able to even them out with the cylinder screws, but it looks like I'm going to have to tweak some of the other variables to get it right, as my vacuum average isn't quite right, and my idle speed is quite high.

My valves are adjusted, I set my butterfly valves with a dial indicator and all are resting on the stopper, my adjustment screws have been cleaned out and the seals replaced, and all the rubber intake boots have been replaced. There aren't many places left to have an intake leak. I currently have my idle speed screw tightened all the way and my idle speed is still high with one of the individual cylinder screws tightened all the way down, so I'm at the limit of the screws adjustment range.

I'm thinking 3 variables are left: intake leak (either in something that affects all cylinder, or in the boot or few seals that each cylinder intake has), butterfly valves are adjusted wrong allowing too much air to go past them when they are closed, idle valve is malfunctioning (stuck fully open), or there is some ECU variable at work (the war chip does have a tab for idle speed). I have some investigation to do this week/weekend.

[HealeyBN7]

Double check the butterfly gap specs. If you read back through the thread I think there was some confusion on how it was quoted in the instruction sheet. It is not clear enough.

The gap should be .1mm-.15mm. That's about .004in - .006in. Mine was happier on the "closed" side of the adjustment.

Here is a photo of the service manual.



Sorry for any rework this caused you. I'll get the pdf updated.

Dean

[Randomg]

I had done the adjustment in the past, so I didn't use your part of the kit for it. I'll go through the butterfly adjustment again and hopefully that fixes it. If memory serves me, I already adjusted it to as closed as possible (I've had trouble getting my idle speed low enough since the rebuild), but I will try to do it more carefully with your tool. I think I'll just put them all at full closed (butterfly resting against the intake runner) to see if I can get the idle lower than 800 rpm to verify that there's not something else that also needs to happen to lower the idle to the right rpm. I'll try to do that tonight.

[tn535i]

Have you checked your TPS to make sure it is sending the idle signal or even jumpered it on the harness side to force the signal. Does the War chip still have the provision to jumper the TPS input and put the computer in open loop mode without idle control. This is where you should be balancing everything anyway.

I'm not a fan of micrometer adjustment of the mechanical linkage. I would unplug the TPS to see where the default ICV position allows it to idle. If too high (>1000) I will close down the t/b's and sort of balance the t/b's with a gauge before fine tuning. I'll bet this is where you are right now. If you have adjusted the t/b's you'll loose it as soon as you tweak anything mechanical and have to repeat. So if that's the case just start over. I would set all the bypass screws about 1-1.5 turns open then balance the mechanical movement of the t/b's using a vac gauge and trying to hit about 900-1000 rpm on a warm engine with the TPS inputs bridged to run in open loop. Once the mechanical adjustment is about right you can proceed back through the individual adjustments. Then remove the jumper on the TPS harness and adjust the mixture on the AFM bypass to get slightly rich. Then re-adjust the TPS switch if needed and plug that back in. It should now be in idle control and dithering and you can use the big idle bypass screw to get the speed you want, but it should be about right.

If the t/b's are too far open the ICV will not close enough to bring the idle down and this may be where you are now.
If the t/b's are too far closed the ICV can't open enough to raise idle on a cold engine and keep it running right.
You need to be at the proper mid point in the ICV range or actually just above mid point with ICV slightly closed on a warm engine IMO.
I don't think you ever get there with measurement of the t/b's.

[Randomg]

My tps works, and I was doing the tuning with it jumpered. I think setting the bypass screws to the default position and using the butterfly stoppers isn't a bad idea to get it close, but another thing to keep in mind is that I'm not just adjusting idle here, ideally you want the throttles all in the same position so that at all other throttle positions are as closely matched as possible. I think the two goals with the mechanical linkage are that the butterflies don't rest against the intake wall (slowly wearing down the aluminum, or potentially binding and getting stuck), and setting them all to the same angle. If their resting angle is not to spec but you can get your idle rpm, afr, vacuum and wot angle correct, I think that's the way to go.

After writing the above I think my current plan is: set bypass screws and idle speed screw to default, adjust using the butterfly stoppers to get the vacuum readings as close as possible, then go in and measure the butterflies and try to set them to the average reading (so if 1-2 is .8, 3-4 is 1.1, and 5-6 is 1.2, I'll try to set them all to 1.03), then check WOT to make sure they're close at the other end of their range, and then use the bypass screws to fine tune. I think this should work assuming that I don't run into the limit of the bypass screw range (maybe I should start with more than 1 turn when doing the butterfly stopper adjustment), but it's possible that one of the intakes is worn so much that in same position as one of the other sets, it just lets too much air flow past the butterfly to let it stay at the same angle as the other two sets.

[tn535i]

I think you have a good plan. Absolutely agree you don't want any of the throttle plates completely closed so checking that out is a good idea. I think if they were fully closed you would need to open the bypass screws way far though. I think the adjustments you'll be making won't make a whit's difference at WOT, maybe at cracked throttle. For that try using the manometer both at idle and with the throttles all just off idle slightly, maybe 1500 rpm or so with a load on it from A/C, and if all is well you should get good balance both ways. If not you may have some slack to dial out of the linkages. Of course all that testing with bridge on TPS so it will not try to dither.

I think we may all measure the closed throttle position slightly differently and that is why I don't bother anymore. Factory trained with factory tools might work but I don't have that option. I tried my best the first time around I did this and got poor results because with the TPS unplugged my engine ran way too fast, maybe 1500 rpm. So I had to close down the t/b's ever so slightly with mechanical linkages in order to get the control range back and also off idle transition right, I think that's about 1000 roughly with TPS unplugged.

The M30 has the exact same issues and I follow the same procedure. Warm engine, unplug TPS, adjust throttle to about 1000 rpm in open loop, adjust and plug back in TPS. On the M30 you are done at that point... easy... maybe check the AFM bypass air.

[Randomg]

Tried again today, followed tn535i's plan, set all the screws to default and used the butterfly stoppers to get them as close as possible first, then tuned with the bypass screws. When I was done and had the right vacuum on the gauge (little less than 30) and all of cylinders at the same place, I was back to where I was yesterday, which is that my idle was still too high.

With the tps connector jumpered, the idle speed was right around 1000 like you had suggested. This was with the cylinder one bypass screw tightened all the way and the 1-2 stopper set to right as it started to move from resting against the intake manifold (I can probably get it more closed with a dial indicator instead of eyeing it, which I'll do tomorrow). I also had the idle speed screw tightened down all the way. I expected to see the idle drop when plugging the connector back into the tps, maybe my idle system isn't working right, I guess I'll check the tps is grounding correctly tomorrow as well.

Not really sure what's going on, I'll go in with a dial indicator tomorrow to make sure the 1-2 set are as close to closed as possible and try again.

I think you're right about WOT, but even if you weren't, I don't care anymore, I'd rather have a good idle than a perfect WOT at this point.

[tn535i]

When the TPS closes at idle is it changing anything? It sounds like you should test it next to be sure you're getting an idle input. First check for voltage at the outer pins, 5vDC IIRC, and then the center pin should be ground (0v) on the connector. Backprobe the connector and plug it back in the TPS and 5v on the idle input (pin 1 I think) must go to 0v when the throttles are closed for idle control. It may just need adjustment or maybe the switch is bad. I've seen several of these TPS have bad solder connections inside after years of thermal cycles.

Idle control on the S38 has always been a bit of a mystery to me and I would not be surprised if some act differently depending on the chip (most are chipped). If the idle loop can 'control' why do you need to adjust the bypass screw on the t/b's anyway. Balancing the t/b's make sense but not adjusting idle. My big screw seems to do little when the TPS is active. In fact I've always thought maybe the instructions I've seen were wrong and should tell you to first unplug the TPS then use the big bypass screw to set the warm idle up to about 900-1000 so that when you plug the TPS back in it controls properly. Sometimes this is in essence what I do. Then when I plug the TPS back in the idle drops a little to about 800. But maybe that's my specific chip ?

Not sure how you would adjust perfect WOT, almost no vacuum and really 80-90% open is probably flowing the same air as 100% open. Above 3500 rpm or so the S38 is just open loop and dumping fuel in based on the AFM and speed map, and making nice sounds. I think if you do get idle right the rest will be fine.

[Randomg]

Went through the whole procedure (I guess I should have done that in the first place) and had better luck. I was able to get my idle down to around 1000 with throttles sync'd at the right vacuum. I think my idle control valve isn't working correctly at this point, but I think I should be ok to fix that later and use the large bypass screw to adjust if necessary without ruining the vacuum syncing of the individual screws. Cylinder 1 and the large bypass screws are tightened all the way, but I guess that's fine if all the measurements are right.

What I meant by perfect WOT is that all butterflies are at the correct angle when resting against the WOT stopper.

For what it's worth tn535i, tuning the idle by the butterfly stoppers didn't end up working well for me. During my drive the on/off throttle transition was worse and my wideband showed noticeably different AFRs at part throttle. Maybe my engine required more variation between the throttles than yours did?

I'll be shipping it back to Healey tomorrow.

[tn535i]

This S38 is a tricky beast IMO. Not the smoothest idle and basically ready to make power with just a crack of the throttle. Isn't that what the ITB's are all about.

It sounds like something isn't right with your idle control though. Maybe the TPS or maybe a sticking or bad ICV? For example, unplug your TPS and see if any on/off idle transitions disappear or anything changes, mine will do that. But when the TPS and ICV are active some slight transitions can happen as you go off idle and the ICV goes back to a home or neutral position. I find it worse on deceleration.

The procedure as I read would have you probably set the t/b's for a slightly open or higher idle with TPS unplugged. Opening the big bypass screw will let more air through and should make the computer close the ICV. If the ICV is quite closed and then goes back to about 1/2 as it comes off idle control at the same time the throttle opens it might make for a bigger bump in speed that you want. Is that what you have now?

If the ICV is more open and closes as it comes off idle you might even get a dip in speed. In this case you will also get a bit more engine break if you close the throttle while in gear as the computer tries to close the ICV all the way down to reduce speed but the drivetrain is trying to turn the engine faster. You'll feel that when you lift off throttle in gear. If the ICV is too far open on normal idle it won't have the range it needs for a cold idle either. So this probably worse than the previous.

Somewhere in between is the best compromise. I'm not sure there is a complete win on the S38 as the computer only knows to try to control or not control idle and the range of the ICV is what it is. I don't think there is any logic for anything based on road speed or gear ratio like a newer car. It may take some experimentation to find the sweet spot you like.

I've been tempted to put a scope on the ICV and watch it's open/close times and transitions. That might be a better way to get the base throttle set about right on a warm engine and then balance from there.

Also, I think as long as you don't adjust the t/b stops or individual bypass screws you are not going to loose your balance made. And what I meant on WOT is the minute adjustments at idle mean almost nothing at WOT, certainly < a 1 degree at idle and the difference of 99% vs 100% is nothing at WOT.

[Pattonky]

I just got through syncing my throttle bodies with a carb tuner. Only 1 and 6 were off at all. 1 was a little high and 6 was a little low. This made a big difference in the idle. The car seemed to kind of cycle before the adjustment and the idle fluctuated from about 870 to as high as 1050. After adjustment she rides more steady between 890-950. I don't think the adjustment of the throttle bodies altered the RPM so much as it allowed the motor to maintain a more constant rpm. RPM taken with Fluke 88. I suppose I am just kind of posting with the hope that this might be useful info to somebody.