Having replaced the idle control vlave to cure stalling I now get (4 months on) an intermittant variation in idle speed.Sometimes nearly stalls but recovers just in time. Can be fine for 2/3 hundred miles and then it will start.What other component could cause this.Lamda sensor?.. or does that just work or not work with no half way point. Fiat 2 lite petrol Ulysse 97. Any ideas. The engine managemnet warning light does not come on.
Thanks
Good luck with this one. I've been chasing the same fault plus a rough idle for a year or two. My theory is that there is an intermittent electrical fault that the ECU is trying to compensate for. (My revs would drop to nearly stalling and then rise to nearly 2,000 a few times before settling down). I bought a current clamp to use with my oscilloscope and found that I was missing a lot of sparks. Either that or the scopes response wasn't fast enough (unlikely I think) or the current clamp wasn't up to the job. Changed the coil and that has made the best improvement out of all the parts I have changed.
I'd look for Air Leaks downstream of the Air Flow Meter (or mass meter if you have one).
This is responsible for 90% of bad idle problems.
When the car is about to stall - the ECU sticks loads of petrol in to keep it going... this makes up for the lack of monitored air - and is why the car fast idles after.
Good luck!
Bob
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