erratic idle trouble

[beetos]

Hi all,
I have an 1990 E36 320i. I have been chasing a problem with a surging idle that starts oscillating so bad that the car cuts out. Other issues are sometimes it misses when started after a run like a plug is not firing or something.

When it starts its episodes of idleing really low and surging I tried unplugging the air flow meter and and smoothed right out. Given this, I thought the plugs and coild were ok and it was the air flow meter. I though is was a little strange that the car would actually run better with the AFM unplugged..?

Thinking that was the problem I tried another AFM and it ran great for a while until I restarted after a run. Now its surging worse than ever, but will once cooled down will probably behave. Again, when its acting up and you unplug the AFM it instantly starts idleing smooth again.

Coils are Bosch and appear to be changed recently. Fuel filter is brand new. Right now I am at a loss. I was wondering if anyone can shed some light on whats going on when I unplug the air flow meter and it runs better?

[s_ribbens]

Have you tried cleaning your Idle Control Valve? Not certain that it's related to your specific issue, but a dirty ICV can cause a searching idle and is certainly not something that always occures. Sometimes it idles great, other times it drops and surges. Worth a shot anyway.

[beetos]

This is weird.......When cold, the idle will shoot up to 2-3000rpm and cut back down to below 1000rpm and then shoot back up. It happens about 3 times a second and continues for about 5 mins before it settles down. I have tried testing the engine temp sensor, cleaned the idle valve, change the airflow meters and it still shite. Lately its started doing it even when warm, I can't drive it anymore as when I put it in drive, it wants to surge forward and the brakes don't work good as there is low vaccum when its surging. Not good.

When it does it, I can unplug the idle valve and still races and surges real bad. I can't see any other way it would get air to do this so maybe the idle valve is sticky, but it does not explain why it would go through this routine every morning. Surely if it was sticking, it would be more hit and miss that what it does now. I am starting to think of bad things like the ECU.

[87esir]

have you check your air intake boot for cracks and you other vacumn lines like the valve cover to intake.

[JohnC]

mine was doing that but i got a new ecu and its still in the shop so im not sure if that fixed it. if you narrow it down to the ecu let me know if you need one and i will get you the info for the guy i purchased mine from, i think it was only around $50

[beetos]

John,
I think it is probably ECU related. Was yours temperature realted, ie, only doing it when cold?