Starting fault: fluctuating revs

[johna]

When I start my M42 powered 1994 E36 318is the revs jump up to about 1500 then drop down to almost stalling speeds, then go up and down a few more times, then stabilise at normal idle speed, about 800rpm.

I have recorded a video (no audio) of a typical start. Please see http://www.youtube.com/watch?v=V9MICx44uHM.

This happens whether the engine is cold or hot and once running there are no idle or running problems whatsoever.

Any ideas on what might be causing the problem?

[johna]

Does no replies mean that not one of the thousands of members of m42club.com have had this problem and know how it was fixed? Or is it E36 bias?

[kowalski]

haha that looks like a really weird deal you got going on. an audio clip would be a little more helpful. does it sound like its missing? when it steadies out does it miss at all? does it have power at idle, can it idle along in first gear? will ti stutter if you just floor it in neutral at idle? if you start it let it idle for a bit turn it off and start it again does it do it?

[RED IS 91]

I would start with the ICV .  Have you checked for vacumn leaks ?? Switched out the ECU maybe ?
How long has it been doing that ?How many miles on your car ?You have to give us more info  than a video with no sound .............
good luck

[gearheadE30]

Check vacuum leaks first. I have a few that I need to get to and it does almost the exact same thing.

[Vladi]

I've got a 08/94 1.8iS that does the exact same thing but only with a cold engine and only on the first start. Mine's not that bouncy, does one loop (up,down,up) and stabilises. All hoses are new. Didn't get to try out another ICV though...

[johna]

It has 160,000km (100,000 miles). I only just bought it a month ago and it has been doing it since I bought it.

It happens on both and hot start but if I keep my foot on the throttle it won't fluctuate.

It only happens at startup. The rest of the time the car idles and drives near perfectly.

If the video had audio you would hear the revs rise and fall and when they fall it sounds like the car is about to stall but then the revs jump up again.

Thanks for the replies!

[Febi Guibo]

+1 on the ICV...
(I need one too!)

[n2motorsports]

can the icv be rebuilt easily? like spray some brake cleaner into it?  they are pretty costly at around ~150 usd.

[johna]

If it is a fault with the ICV then wouldn't the idle be bad all of the time, not just at startup?

[Febi Guibo]

i think the ICV operates differently when the engine is cold vs. after its warmed up

[johna]

The problem occurs whether the engine is cold or hot.

[kowalski]

you can test is pretty easily. hook 12 volts up to it and if it shuts/opens then it works. If not i have an extra i'll sell ya.

[RED IS 91]

If the icv was bad then it not run well hot or cold .A good cleaning and test maybe all it needs .

[Vladi]

If it is a fault with the ICV then wouldn't the idle be bad all of the time, not just at startup?

Probably i'm going to test another ICV next week so if you don't fix it by then i'll come back with a result.