Surging Idle when warm 1987 325e

[spencerhitch]

Hello Bimmer Forums,

On cold start, no surging is present, the idle is relatively stable. After about 30 seconds, it begins to surge cyclically, regularly and constantly.

Y'all got any ideas?

I'll update the thread as I continue on the untested list.


Tested:
0. Spraying carb cleaner around hoses didn't affect idle speed
1. Coolant temperature switch, successfully shows resistance at temperature
2. Coolant Temperature sensor, shows correct resistance for temperature
3. Idle Control Valve (ICV), tested in place, shows resistance across endpoints
4. ICV, removed, cleaned tested with jumper cable to endpoints, successfully closes and opens when current applied or removed
5. Surging remains unchanged when cable removed from ICV


Untested:
0. Cable from ICM to ICV
1. ICM itself
2. Throttle Position Switch (TPS), requires removing throttle housing


My youtube video:
https://www.youtube.com/watch?v=BFzfckwo4EQ


Similar issues described here:
https://www.bimmerforums.com/forum/s...-idle-question


Similar issue depicted here:
https://www.youtube.com/watch?v=UjCfefcEJBQ

Best,
Spencer

[superj]

you have a little vacuum leak somewhere. but some people also have had trouble with the idle control valve being dirty so they popped it off and sprayed the heck out of it with cleaner and that fixed it.

[spencerhitch]

Update,

Tested,
0. Wires from ICM to ICV, these have successful continuity (pins 1 and 5)
1. Inputs to ICM as detailed in Bentley, all are functioning as expected
2. Full throttle position switch working as expected. Does not require removing throttle housing, just the air intake boot.

Conclusion. I ordered a new ICM from FCPEuro and it's coming next week. I'll let you know if that solves the issue.

Seems like the ICMs go bad on late 80s etas. Given I'm working with a 1987 325e this makes the most sense.

If this fails, I'll take it to a shop for a smoke test I suppose.


Here's the Bentley excerpts:
https://imgur.com/a/XasSXsV

Also useful is the knowing the wiring for the ICM input:

Wiring colors diagram


Pin 1 blue/red
2 green/yellow
3 green
4 brown
5 blue/black
6 white
7 green/black (auto tranny), green/yellow (manual tranny)
8 not connected
9 blue/white
10 blue/green
11 brown/red
12 brown/blue

source: https://www.bmwcca.org/forum/index.p...e-pinout.2606/

[spencerhitch]

Update: New ICM didn't change the behavior. I took this into the shop, they tried a buncha troubleshooting and eventually allegedly switched the parity of the plug into the ICV, which resolved this.

Does not answer why this behavior began to begin with.