High Idle after manual swap

[hayden_duffy5]

Hey Guys,

I recently manual swapped my 88 535is from automatic in Late October of 2022 with a G265/6. After the swap my idle is much higher than before and I can not seem to figure it out. When the car was an automatic the idle was never super steady but stayed anywhere around 700-900rpm.
After the swap the car felt and drove amazing except for the fact that the idle (warm and cold) would consistently sit at 1200-1300rpm. There have been times when it would drop back to its normal idle speed but usually goes back up after driving then back to neutral (such as going from one redlight to another). At first I thought maybe it could be the ICV so I took it out and cleaned and sprayed with wd40. After that no change. So now I’m thinking it maybe a vacuum leak or something to do with the computer.

If any of you have any idea what may be causing the high idle or have experienced this yourself after a manual swap, any help and input is appreciated.

Thanks

[kojo96]

Automatic and manual have different TPS sensors, double check it'sworking correctly, that might be your problem. Also check you ICV.

[Mike W.]

Too much air (vacuum leak) or the throttle is partly open. More likely the latter. The throttle cable should be slightly slack, have just a little play in it and not be preloading the throttle at all. The TPS should show closed at idle too.

[Shawn D.]

Automatic and manual have different TPS sensors, double check it'sworking correctly, that might be your problem.

While they are different, the difference is related to WOT signaling, not idle position. The idle position switch function could indeed be the issue.

[Shawn D.]

BTW, OP, did you do anything to replace the WOT function? On automatics, it's provided via the transmission control unit, so if you do the swap and don't change to a manual engine harness and manual TPS, you need to wire the WOT signal to see ground at full throttle. I used the kickdown switch and wired it to ECU pin #3.

[hayden_duffy5]

I know its been a while, but thanks for the replys.

I preformed a smoke test on my m30 to check for vacuum leaks. I found two very small leaks. One coming from the back of the ICV(where the connector is) and another super small leak coming from the butterfly shaft of the throttle body where the coil spring is. I then replaced the ICV with another known good one that I have. When I smoke tested it again with the good ICV it did not leak however the car idled significantly higher (3000rpm) so I decided to put the original back on. I think it is safe to say that the issue is not the ICV. Throttle cables have slack ass swell.

So now my question to you all is…

For the TPS what and how do i need to check in order too see if it is closing all the way at Idle?

I do not recall the mechanic telling me about doing any wiring for WOT. Should i check for this first? Do you have any more detailed information on how to wire the WOT signal?

Thanks

[Shawn D.]

For the TPS what and how do i need to check in order too see if it is closing all the way at Idle?

The idle switch should have continuity at zero throttle and be open just barely off of zero throttle.

I do not recall the mechanic telling me about doing any wiring for WOT. Should i check for this first? Do you have any more detailed information on how to wire the WOT signal?

Well, you don't want to redo work that has possibly already been done, right? You really don't need much "detailed information" other than connecting pin #3 to the terminal on the kickdown switch; just fish out the wire and connect it to the terminal, and if you need to extend the wire, 18- or 20-gauge will suffice.

[hayden_duffy5]

Thanks Shawn, Ill take a look into it.

[hayden_duffy5]

Alright….

I’m back and here is what i have been up too. I took the car to my mechanic who is very knowledgeable when it comes to e28’s. He did the wiring to the kick down switch and the car seems to idle better still a little bit high but better. He then performed a smoke test to check for vacuum leaks, the ICV had smoke coming from around the connector. So he replaced the ICV with one he had lying around. The car would idle very rough bouncing from 900ish-1300rpm rapidly(sounded like a big cam v8) and when I drove it the revs would hang. For example i would clutch in to downshift and the idles would stick at whatever rpm i was at before pressing the clutch. So this made the car very unpleasant to drive. I then ordered a NEW “OEM” ICV made by “Hamburg Technic” from ecstuning, installed it and it was worse than the other two ICV’s. It would rev on its own and made it terrifying to drive(couldn’t even make it out of the neighborhood).

My question to you all is if you have experienced this and what did you do to fix it?
I am now wondering if it could be another part of the intake system such as the MAF or throttle body.

Any suggestions are appreciated. I have been dealing with this for too long.

Cheers!