Annoying Rough Idle Issue

[wkohler]

1987 535is 280,953 miles

I've done a lot of searching over the last day or so, but I couldn't find anything that really fit with this issue.

I've noticed for the last 8-10k miles, the idle hasn't been the pinnacle of smoothness. Even for M30 standards, it's rough. I didn't worry much about it since once I had some time, I had some things planned.

Since I started having an issue where the car was running excessively hot under load, but reasonable at idle or low load conditions (around town), I decided to redo the cooling system, along with replacing all ignition components (except coil) and the o2 sensor (since the Miller MAF relies on the o2 sensor input and will not run open loop). After all, none of that had been done in the 40k I've had the car.

So, here's what was done:

Valve adjustment with new valve cover gasket
New plugs (WR9LS)
New Cap and Rotor
New plug wires
New o2 sensor ($120 - ouch)
Replaced throttle cable grommets
Oil and filter change
Air filter

All coolant hoses
Thermostat
BMW coolant

So, after all of that, the car still needs a radiator (decided against previously when we found the pulverized thermostat).

As to the idle issue, it idles steady at 750 - with or without the air conditioner on. The problem is just that it's very rough, and that's not just from me sitting in the car saying, "Ow," which some would dismiss as my urethane motor mounts. The motor looks as though it's working to exorcise demons. There is no change with the clutch disengaged. Engine temperature has no bearing either.

Aside from that, the major concern comes in when slowing down to a stop (clutch in, transmission in neutral and brakes engaged), the car will stall. This only happens with the air conditioner on. When it's off, this same scenario results in idle dropping to 500 rpm (indicated) and settling back at 750 once stopped. On very rare occasion, the idle will drop to 500 while sitting at a stop light and start shaking violently. It is reminiscent of fuel starvation (though there's more than 1/2 tank of fuel at all times and both pumps are confirmed to be working).

I checked all vacuum lines. They're all in place and show no signs of deterioration. I have not touched the idle control valve since I'm not dealing with a high idle or a fluctuating idle. Everything was reinstalled properly. I also unplugged the ECU.

Off idle, this car runs like a raped ape. It is much stronger than other 535s I've driven with half the mileage. There's no stumbling or hesitation all the way up to 6200 rpm.

I'm obviously at a loss. Hopefully that should be sufficient info. Thanks in advance!

[wkohler]

MAFs have been known to cause idle issues due to low flow across the wires. I'd look to see if there are any vacuum leaks, such as the ICV-to-manifold hose or any of the lines that connect to the plenum.

After installing the MAF, idle was very smooth. I checked all of those hoses (replaced when new ICV was installed before my purchase).

I just started the car and was going to try a couple of things and I noticed fuel was pouring out of the CSV onto the left side of the block, but the car was actually idling smoothly (will replace it and the fuel line to it Monday). I need to do some reading on the CSV though, but could that have any bearing on idle once it's done doing it's thing, especially if there's an obvious fault?

[Shawn D.]

I need to do some reading on the CSV though, but could that have any bearing on idle once it's done doing it's thing, especially if there's an obvious fault?

It certainly could have an effect on idle if it were coming on when unnecessary -- the mixture would be over-rich.

[Kyle in NO]

You need to clean the inside of your throttle body with brake cleaner and a tooth brush, then set your throttle plate clearance. It should not be touching the TB wall like it likely is right now. Then, adjust the TPS so it clicks properly with the throttle plate in its new position. Yes, you will probably move it that much. There is some sort of minuscule measurement in the Bently, but whatever. You don't have to be 100% precise on where you set the plate, I just move the bracket to where the linkage hits its stop before the plate touches the housing. I call the clearance about "one cunt hair". The ICV will take care of the rest. The lack of clearance is what causes the stalling, the ICV doesn't react fast enough to do everything on its own.

This has cured your symptoms on every M30 I've done it on.

[Rich Euro M5]

You need to clean the inside of your throttle body with brake cleaner and a tooth brush, then set your throttle plate clearance. It should not be touching the TB wall like it likely is right now. Then, adjust the TPS so it clicks properly with the throttle plate in its new position. Yes, you will probably move it that much. There is some sort of minuscule measurement in the Bently, but whatever. You don't have to be 100% precise on where you set the plate, I just move the bracket to where the linkage hits its stop before the plate touches the housing. I call the clearance about "one cunt hair". The ICV will take care of the rest. The lack of clearance is what causes the stalling, the ICV doesn't react fast enough to do everything on its own.

This has cured your symptoms on every M30 I've done it on.

x2

Chris,

What Kyle is telling you to do is the same as setting the base idle on a Volvo, except the M30 TB doesn't have the adjustable bypass like the Volvo TB does.

Rich

[wkohler]

This issue has been resolved. Today, the 535 got a South African radiator for no apparent reason, a new hose between the rail and the cold-start valve, and a new hose from the ICV to the manifold. I wanted to rule out that ICV hose, but it wasn't the issue, despite it being hard as a rock.

Just as Kyle said, and told me when I was dealing with high idle with the 533, the throttle plate clearance was the key. With that set, the idle is rock-solid at 750 rpm and much smoother - M30 smooth. Gone is the stalling. There's no dip to 500 rpm on deceleration, either.

So, I just wanted to say thanks for the replies and that I'm a reasonably-happy person.

I also have to say that this also made the car feel even better off idle, too! It now runs like a twice-raped ape.

[pldlnr]

I would think the ape would have a wilder reaction after the first rape. The second and third time it starts to become familiar.

[wkohler]

I would think the ape would have a wilder reaction after the first rape. The second and third time it starts to become familiar.

See, I was thinking that the ape would be really sore and probably couldn't run very well, so the whole analogy (no pun intended) doesn't work well.

[pldlnr]

Good stuff.

[clemoyne]

So I'd like to thank you guys for fixing my idle issue...I've had a "return to idle" issue since I bought my car. I never really tried to fix it until I saw this post. Sure enough, cleaning the throttle body and tightening up the throttle cable a little bit cleaned it right up!

[Kyle in NO]

So I'd like to thank you guys for fixing my idle issue...I've had a "return to idle" issue since I bought my car. I never really tried to fix it until I saw this post. Sure enough, cleaning the throttle body and tightening up the throttle cable a little bit cleaned it right up!

Damn it...do it right! Tightening the throttle cable is NOT the way to fix the problem.

[wkohler]

So I'd like to thank you guys for fixing my idle issue...I've had a "return to idle" issue since I bought my car. I never really tried to fix it until I saw this post. Sure enough, cleaning the throttle body and tightening up the throttle cable a little bit cleaned it right up!

Damn it...do it right! Tightening the throttle cable is NOT the way to fix the problem.

x2

[clemoyne]

Relax guys, I guess I didn't know how to "do it right".

I couldn't see another way to adjust the throttle plate clearance.

[Kyle in NO]

The throttle plate stop on the back side of the throttle body is adjustable. Loosen the 10mm nut, move the stop, tighten the nut. Then, set the TPS so it clicks in its new position. Then, have someone hold the pedal to the floor while you look at the throttle plate. Its not gonna be horizontal, I guarantee it. Loosen or tighten the cable while the pedal is to the floor to make the plate perfectly horizontal, and you now have a perfectly adjusted throttle plate...

You need to clean the inside of your throttle body with brake cleaner and a tooth brush, then set your throttle plate clearance. It should not be touching the TB wall like it likely is right now. Then, adjust the TPS so it clicks properly with the throttle plate in its new position. Yes, you will probably move it that much. There is some sort of minuscule measurement in the Bently, but whatever. You don't have to be 100% precise on where you set the plate, I just move the bracket to where the linkage hits its stop before the plate touches the housing. I call the clearance about "one cunt hair". The ICV will take care of the rest. The lack of clearance is what causes the stalling, the ICV doesn't react fast enough to do everything on its own.

This has cured your symptoms on every M30 I've done it on.

[warrhed98]

a couple years later, but this info was super helpful!

I'm having an idle issue with my e12's turbo m30b35. Won't idle...dies when the RPM drop..all that nonsense.
My dad noticed today that the throttle had some slack in it, and that the small white bushing was worn..I'll try adjusting it tomorrow and see how it goes!

[wobbledink]

Thank You !

I know this is an old topic. Kyle in NO is a genius.

I did this yesterday and this made a big improvement. The throttle plate was touching and way out of adjustment.

Thanks for the information!!!!

[Amos830]

Well now I'm all curious if mine is set properly.

[wobbledink]

I have had my car since May and it had a pretty low idle at 500 RPM. I had a problem where when it rained it would run like it was missing. I kept thinking water was getting in the fuel some how. Sometimes I could smell fuel in the cabin after the car was parked for a few hours.

Friday on a nice sunny day it started stumbling and missing on the way to lunch. I found a small fuel leak at the firewall side of the fuel rail. I fixed that, and while I had the bellows and stuff off I did this adjustment as Kyle describes, paying particular attention to the fine RCH clearance. I was wary of adjusting stuff that has yellow locking paint. But after close inspection I could tell someone messed with the screws before. I am not a mechanic, but these instructions were easy to follow.

My idle looks to be about 750 on a cold start, and maybe 650 after warm, up based on the dash tac. I’m not sure how accurate that is, but it sure runs much better and seems about right. I’m wondering how the humidity after a rain would amplify the fuel leak. Or maybe I am tying the two together when they are not related. Come on thunderstorm!

Cheers!

On an afterthough. Kyle used a OCH... I used a RCH. Which is a red one and slightly finer.

[pleasefixitup]

just found this thread, Kyle is a Genius. I always thought the throttle plate had to be 100% closed and tight. Going to adjust to 1 "c&nt" hair and see how things go.

[orignal teile]

did this today on my car, as over the weekend, after changing the intake bellows, it wouldnt idle worth a damn, by itself. as i did it solo, first time though, i did it a little too high, and the idle was at 1k rpm, after barely at 550 rpm before (when it would idle). so as it was running, i let it down a little bit, and held there nicely at ~800 rpm. after revving it in neutral, the RPM never drop below idle, problem solved

[pleasefixitup]

did this today on my car, as over the weekend, after changing the intake bellows, it wouldnt idle worth a damn, by itself. as i did it solo, first time though, i did it a little too high, and the idle was at 1k rpm, after barely at 550 rpm before (when it would idle). so as it was running, i let it down a little bit, and held there nicely at ~800 rpm. after revving it in neutral, the RPM never drop below idle, problem solved

[Mike W.]

So, I just wanted to say thanks for the replies and that I'm a reasonably-happy person.

You saw it here, Chris saying he's reasonably-happy! Even if it was back in '09. Just goes to show he's not always down on things.

[shagrath]

Maybe Kyle's input should be made a Tech sticky or FAQ?

Inevitably I will get another m30 car. SO I am in for this thread and info. Thanks Kyle!

[Loach]

The throttle plate stop on the back side of the throttle body is adjustable. Loosen the 10mm nut, move the stop, tighten the nut. Then, set the TPS so it clicks in its new position. Then, have someone hold the pedal to the floor while you look at the throttle plate. Its not gonna be horizontal, I guarantee it. Loosen or tighten the cable while the pedal is to the floor to make the plate perfectly horizontal, and you now have a perfectly adjusted throttle plate...

You need to clean the inside of your throttle body with brake cleaner and a tooth brush, then set your throttle plate clearance. It should not be touching the TB wall like it likely is right now. Then, adjust the TPS so it clicks properly with the throttle plate in its new position. Yes, you will probably move it that much. There is some sort of minuscule measurement in the Bently, but whatever. You don't have to be 100% precise on where you set the plate, I just move the bracket to where the linkage hits its stop before the plate touches the housing. I call the clearance about "one cunt hair". The ICV will take care of the rest. The lack of clearance is what causes the stalling, the ICV doesn't react fast enough to do everything on its own.

This has cured your symptoms on every M30 I've done it on.

Okay, I'm confused here. It's possible I'm missing a stop piece on the other side of this cable. But I don't see how to adjust the cable when the pedal is pressed to the floor, to adjust the stop for when the throttle plate is perfectly horizontal. The only way I can get that thing to be perfectly horizontal, is to adjust it by loosening the 10mm as explained, and then moving that bracket to where the plate is completely horizontal and hits the stop, tightening it there, and then when I let off the pedal I adjust the plastic piece on the cable to open up that "one cunt hair" amount of plate clearance.

So as far as I'm concerned, unless I'm missing something or I'm completely overlooking something, I'm having the same issue as clemoyne, I don't see any other way to get the plate perfectly horizontal, unless I tighten that bracket to first get the plate horizontal, then adjusting the plastic cable piece to get the clearance at idle. I can see how you can adjust the 10mm, adjust the bracket to where it has the clearance when it hits the stop at idle, but the plate isn't horizontal then, and I don't know how to adjust the cable to get it horizontal from there.

[Kyle in NO]

You are trying to do it backward. Have a helper hold the pedal to the floor. Look at the throttle plate. If the plate is under horizontal, tighten the cable until you achieve horizontal. If the plate is over horizontal, loosen the cable until you achieve horizontal. Adjustments are to be done with the cable slack, not with the pedal held down. Adjust, check, adjust, check, until you get satisfactory results. Don't forget to tighten the tiny jam nut on each cable adjuster when you are done.

The throttle stop is what you are adjusting when you loosen the 10mm nut and bracket.