Idle Surge issues *528e M20

[Mike From T.O]

I just picked up a E28 528e with a M20 & i am having idle surge issues. Previous owner told me it needed a battery, gas, & spark plugs.

I addressed all 3 things, car started up no problem at first idle was about 600 - 700rpm, after letting it sit for 10 minutes the idle was sitting at about 1200RPMs. It's developed a issue where it idle surges.

Next day I do a oil change, Idle is fine again on cold start 600rpms, took it for a drive, warmed it up & I put it in park the idle started surging 500-1200RPMs in park back and forth. It would die out depending on when you hit the gas on a drive. I restarted the car, then its fine... Go for another drive, the idle starts to surge between 500-1000RPM’s or between 600-1200rpms afterwards.

On cold starts the idle will sit at 1200 -1300RPM’s the car seems ok, I can flick the lights on & off helps the draw with the idle surge the first and the car not dying out which happens sometimes while driving.

Additionally, I’ve noticed the coolant temperature switch is not plugged in and I didn't have one installed on my car, I am curious if this could also help with the idle surging when getting to a certain temperature point?

Performed a smoke test, addressed leaks... started the car back up and the idle got worse than before. It seems to be my car is running better with air leaks and is running rich. Once the car was up to temperature, the car wouldn't even start up, I disconnected the MAF & it started up again.

Some extras I've picked up are an ICV, ICM, TPS, a new CTS, & cold start valve. I'm close to pulling trigger on a new fuel pressure regulator and 02 sensor. I haven't changed anything yet & Fuses are all good.

Any Sort of input will help!!! I've attached the link for my Imgur, with pictures & videos. Thanks in advance!!!!
link : https://imgur.com/gallery/e28-wild-with ... es-lH9WxSh

[Mike W.]

M20s aren't my strong point so I'll let others chime in and just reply if they don't.

But welcome to our group and wow, nice sharp looking car! At least from a distance and hopefully closer up.

[Mike From T.O]

M20s aren't my strong point so I'll let others chime in and just reply if they don't.

But welcome to our group and wow, nice sharp looking car! At least from a distance and hopefully closer up.



Yeah she's in great shape! Underbody is clean, engine bay is in great shape all interior bits and the radio works! Really hard to find one running and all in one piece without having to donate a kidney I'm located out in Toronto, Canada.

Here's another picture, hopefully someone with a M20 will chime in and I can dive deeper into this issue of mine.

[Mike W.]

M20s aren't my strong point so I'll let others chime in and just reply if they don't.

But welcome to our group and wow, nice sharp looking car! At least from a distance and hopefully closer up.

Yeah she's in great shape! Underbody is clean, engine bay is in great shape all interior bits and the radio works! Really hard to find one running and all in one piece without having to donate a kidney I'm located out in Toronto, Canada.

Here's another picture, hopefully someone with a M20 will chime in and I can dive deeper into this issue of mine.

Posting pics gets a little quirky, but not too bad, in other words it didn't come thru. Check out CEK's FAQ.

https://www.mye28.com/viewtopic.php?f=1&t=147488

[Mike From T.O]

Thanks Mike, I'm still trying to figure out how to use the forums, one day at a time If anyone with a M20 or with previous idle surge issues can chime in that would be amazing, any information helps!

[kojo96]

Sure sounds like your idle control module. Notorious for erratic idle in these models. It's located in your glove box, above the ECU. Drop the ECU and you'll see it, just off to the left. A single 10mm bolt holds it in, a multi wire connector.
If it's Black, it's the original, if it's green, it's been replaced.
These modules are known/prone to bad solder joints and cause erratic idle, all the time.

[Mike From T.O]

UPDATE*

I ended up changing out the ignition cables, distributor rotor and cap. Also added a temp switch, since my car didn't have one installed.

The car seems to be running a lot better. Idle is now being held around 600RPMs. With a very slight movement, but it could be vacuum related.

Another issue I'm having is when I'm driving while the idle comes down if i punch the throttle the car stalls out and shuts down.

Seems like I'm almost getting to the bottom of this... Any other suggestions at this point?

Maybe its the high pressure fuel pump, or something along the lines of that?

[Mike From T.O]

Sure sounds like your idle control module. Notorious for erratic idle in these models. It's located in your glove box, above the ECU. Drop the ECU and you'll see it, just off to the left. A single 10mm bolt holds it in, a multi wire connector.
If it's Black, it's the original, if it's green, it's been replaced.
These modules are known/prone to bad solder joints and cause erratic idle, all the time.

I Have a spare one, the car idle seems to spike sometimes as well. It will be fine at 600RPM when warmed up, but randomly jolt not like the idle was before when it was bouncing all over the place. From my understanding all of the maintenance items were overlooked on my car, so it looks like ill need to address some things before i can start getting to the bottom of it.

So far I've ordered new but not installed :
02 sensor
intake hose
air filter
fuel pressure regulator
coolant temperature sensors for dash and ECU
brand new temperature switch, the one i used for testing was a used unit which was having problems opening and closing at temp.

Debating if i should pull the trigger on
ignition coil
throttle postion sensor
and a new fuel filter with high pressure fuel pump

Maybe these will clear up my car dyeing & stalling out while on throttle too.
On idle in drive, if i just punch the gas it will die, even almost full throttle it will die LOL. However if i just do it a bit or half way i can get moving.

Though on the positive, Seems the idle situation is sorted for the most part.

[Mike From T.O]

* BIG UPDATE

Well we have great news! The 528e has finally been sorted out.

Fortunately i have some great mechanics who found two ECU's for my 528e, we swapped in the second one and the car hasn't missed a beat since.

No issues of the throttle dying while driving, or the Idle surging all over the place.

Issues noticed :

Car running rich, idle surging, and vehicle would stall by itself, die on full throttle or when idle is coming down and punching the gas.

New parts in order that solved issue :

Did a smoke test, the car was leaking from a lot of hoses. Installed New hoses closing off any vacuum leaks, which actually made it run worse.
New cap, rotor, spark plug, & spark plug wires, fixed the running rich issue.
New coolant temperature switch, it didn't have one when i purchased the vehicle so we installed one and it made it better when hot but not perfect.
The vehicle was still spiking, so i ended up changing the ICM, still to no avail the issue was not fixed.
However my mechanics thought it would be a great idea to try some new ECU's. The second one we popped in fixed all the issues right up.

Any parts I ordered I can now keep as spares! Thanks for the help guys, hope this will maybe help someone else out in the future with similar issues!

[gwb72tii]

Thanks for telling us how you fixed it. I wish more people would post what the actual resolution of a problem was so we all know in the future what to do.