Hello,

I am puzzled a bit.My car is V40, 2000, 1.8 (volvo engine), it has that "erratic idle" problem. It all started quite unexpectedly. I was driving back home and suddenly rpm dropped down and stalled (during idle) - - - > ignition - - - > acceleration - - - > again sudden stall from 1000 rpm to 0rpm). Again and again. After a while it became better though idle was very rough. "Service" light and "Engine" light appeared. I got home. Cleaned throttle body, IACV. Became a bit better.
After these cleaning things car starts like that :
>1000 rpm at the beginning, then becomes stable at around 1000 rpm. It is like that for about 5 minutes (almost unnoticable rpm changes, if any). When i start to drive my car (accelerate) - everything is fine until first stop: it idles erraticly, rpm from 900 to 800. After a while, when i get closer to work it idles around 500-600 rpm with tendency to get lower and lower. Finally it is around 300 rpm and 600 rpm (changing like in two phases each phase lasts about 10 seconds: 300rpm (for 10 seconds) then 500 rpm (for 10 seconds) then, again, 300 rpm (for some seconds) etc.

and i thought (maybe stupid tought, but.. oh well) why not disconnect some air sensors and see what happens.
1. MAF - car shuts down rapidly.
2. ICV sensor - Extremely rough, unstable, idle.
3. Throttle position sensor - nothing changes and erratic idle still present.


I am puzzled of what may it be. Engine works like a clock, very rhythmic and smooth sound. Maybe it is Throttle position sensor, maybe lambda sensor ? It is probably not connected anyhow , but when i open my fuel tank it makes that very interesting sound "pffff) like air is coming out of there...