Please help with 1984 733i Idle Surge. I have replaced everything at this point

[Triumph003]

Hello Folks,

I have done some pretty extensive forum searches and replaced everything I can think of and recommended to get my 1984 733i to idle without surging. It runs fine down the highway and idles fine when cold but as soon as it warmups it surges badly. Here are the parts that have been replaced:

1. New Idle Control Module from Programma
2. New TPS sensor
3. New Idle Air Control Valve - pain to find but I got one that does work
4. New vacuum lines, hoses
5. Passed the smoke test and no massive air leaks and I cannot even find any small ones. I ran the test multiple times.
6. Cleaned the MAF and seems to be functioning fine.

I am at a loss.. I have no idea anymore and my local BMW friend/enthusiast is stumped as well. Was thinking maybe the ECU but it runs fine at highway speeds etc.. and the ICM was replaced.

Please any thoughts on this as I am now thinking of rolling it off the hill behind my shop.

[mdrogersmdr2]

You could eliminate the cold start valve as an issue by pinching off its fuel supply (I did it with a pair of needle nose vise grips with a rubber hose over each jaw). Also check the coolant temperature sensor resistance at various temperatures to verify it is in spec. If that doesn’t work you can test the wiring to the ICM.

Agree it probably isn’t the ecu but not sure. As somewhat of an aside, my ecu was malfunctioning and caused the car to stumble under light throttle around 1,500 rpm but it did not impact the idle.

[Hit Man X]

Verify fuel pressure.

Programma makes crap, just FYI.

[Mikebear79]

I just had my ICV out to clean it with brake cleaner to get rid of a slowly oscillating idle problem, which helped mostly, but one thing I noticed was that when the car was idling and warmed up, I disconnected the connector to the ICV and my car immediately started to idle way up and way down in a rhythmic pattern. Kinda sounds like your problem.