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!

[Foonfer]

Hi there-  I would have loved to find this topic before, if only to commiserate...  I was in the EXACT same boat, EXACT same symptoms, for almost a year. M30B35 swap, with a Getrag 265/6.  Not sure if the M30 came originally with an auto or a manual, I'm guessing an auto.

Things that seemed to help or might have helped but whose contribution wasn't really noticeable:
1. Checking every bit of vacuum
2. Replacing rubber intake parts (the elbow after the air filter, the ribbed tube where the ICV is attached to)
3. Replacing the AFM with one purchased directly from ProgRama
4. Replacing fuel pressure regulator
5. Testing out a loaned DME
6. Replacing the ICV with a used Bosch unit purchased on Ebay (no difference) and with a Löwe unit purchased new (no difference)

Things that I think fundamentally changed the game:
1. Replacing the Coolant Temperature Sensor (idle was OK when cold, started surging the moment the engine warmed up).  I think these parts are very similar for the M30B34 and for the M30B35 but part numbers might be different - check RealOEM.
2. Installing a $35 Chinese ICV purchased on Ebay (brand: ISUMO) - I'm chalking this up to "luck of the draw".  I have maybe 1K miles on this ICV, and have no expectations on its longevity - we'll see.
3. Installing hose clamps at both connection points of the ICV.

Currently, my idle tends to stay fairly stable at 1000rpm.  After a hot run (say, 1hr at highway speeds) idle tends to go up a bit, 1100 or so, but remains fairly stable and tends to gradually come down.  Most importantly it doesn't "keep" while shifting gears, it comes down when I let off the gas and press the clutch... which, same as the OP noted, felt very weird when combined with the surging idle.

I noticed that the only "OAC" option for an ICV in the usual parts dealers these days is branded "Hamburg Technic".  I have not tried it but sounds like the OP did, with bad results.

Frankly if BOSCH came out with a $800 ICV that is good for another 30 years, I'd be hitting that checkout button so hard.




 

[turbodan]

1k is still too high.

TPS and throttle body adjustment is where I would focus. Make sure the TPS is sending a "closed" signal when the throttle is fully closed. Make sure the throttle is not hanging open from insufficient free play on the throttle cable or cruise control cable.

I know the autos had a park/neutral signal that the DME is looking for to cut back on the idle speed. If it thinks it's in gear it's anticipating additional load from the torque converter. Once you remove the shift lever you need to jumper the wiring here to tell the DME it's in no-load idle mode.

I might have to go look at the ETM as I can't remember if this is only for motronic 1.1 or if it applies to the B34 version of motronic as well.

[Foonfer]

1k is still too high.

TPS and throttle body adjustment is where I would focus. Make sure the TPS is sending a "closed" signal when the throttle is fully closed. Make sure the throttle is not hanging open from insufficient free play on the throttle cable or cruise control cable.

I know the autos had a park/neutral signal that the DME is looking for to cut back on the idle speed. If it thinks it's in gear it's anticipating additional load from the torque converter. Once you remove the shift lever you need to jumper the wiring here to tell the DME it's in no-load idle mode.

I might have to go look at the ETM as I can't remember if this is only for motronic 1.1 or if it applies to the B34 version of motronic as well.

I checked the TPS (which was bought new for the swap) and voltages and such were OK, and there's play in the throttle and the CC cables... but I have always suspected there could be something funny there.

The auto vs manual thing is a bit mystifying, because in the end both autos and manuals came with the same DME (both the OP's 535i and my M30B35 swap)... if the auto-to-manual situation is what is causing the idle issues (both on the OP's car as on mine) then it sounds like there would be something off with the wiring, some (minor?) tweak that is needed so the DME understands it is talking to a manual and not an auto.

Only thing I am (almost) sure of, is that the engine operating temperature plays a part in this whole issue (the OP described the exact same behavior - Idle is perfect when cold, and then the issues start showing up when engine is warm).

[turbodan]

1k is still too high.

TPS and throttle body adjustment is where I would focus. Make sure the TPS is sending a "closed" signal when the throttle is fully closed. Make sure the throttle is not hanging open from insufficient free play on the throttle cable or cruise control cable.

I know the autos had a park/neutral signal that the DME is looking for to cut back on the idle speed. If it thinks it's in gear it's anticipating additional load from the torque converter. Once you remove the shift lever you need to jumper the wiring here to tell the DME it's in no-load idle mode.

I might have to go look at the ETM as I can't remember if this is only for motronic 1.1 or if it applies to the B34 version of motronic as well.

I checked the TPS (which was bought new for the swap) and voltages and such were OK, and there's play in the throttle and the CC cables... but I have always suspected there could be something funny there.

The auto vs manual thing is a bit mystifying, because in the end both autos and manuals came with the same DME (both the OP's 535i and my M30B35 swap)... if the auto-to-manual situation is what is causing the idle issues (both on the OP's car as on mine) then it sounds like there would be something off with the wiring, some (minor?) tweak that is needed so the DME understands it is talking to a manual and not an auto.

Only thing I am (almost) sure of, is that the engine operating temperature plays a part in this whole issue (the OP described the exact same behavior - Idle is perfect when cold, and then the issues start showing up when engine is warm).

On the M30B35 Motronic DME it is looking for 12v to pin 42.  In the absence of this signal, it assumed you're in gear.  I would wire 12v in and see what you get.  I see that the ETK shows the same part number for auto or manual on the B35 DME but the coding is different.  If you get a factory MT DME it won't require that 12v signal.

For the B34 DME it gets the P/N signal through pin 28 except it's straight to ground.  Factory automatic cars are wired to ground pin 28 through the shift lever switch in park or neutral.  Factory manual cars have pin 28 hard wired to ground. 

I would encourage you to download the ETM from a place like e28goodies and double check me on this.  It's under the "injection electronics" section.  I think there's a good chance this could rectify the hanging idle issue.