Originally Posted by GialloEvo94
As Simon said, most likely suspect is the MAF (you generally get the same idle bouncing behaviour with the MAF unplugged). You have a phase 2 (CF2 engine) so if you get a new MAF then get a Vauxhall one (Bosch part number 0281002180) as they're cheaper than the Alfa one (Bosch part number 0280218019). It's got an identical internal sensor (Bosch part number F00C2G2030) to the Alfa one and people who have recently fitted the vauxhall one report that the housing tube is also a direct fit so it means no messing around swapping the internal sensor into your exising tube. I've seen new Vauxhall ones advertised for around £65. Also try your local motor factors or Andrew Page for cheap prices. As already mentioned, only get a genuine Bosch one with the "Bosch" logo moulded into the side and don't be tempted by an aftermarket (Chinese copy) one.
If a new MAF sensor doesn't fix the problem then you will need a new Idle Stepper Motor which is the black plastic sensor mounted to the side of the throttle body that controls the actual idle speed. These are generally pretty expensive though (well over £100) and you would need to have it calibrated to your engine ECU once fitted.
the idle stepper motor (is this the idle control valve?) and why does it have to be calibrated to the ECU (as i have replaced lambda, maf, idle actuator/control valve (the many names for it) and cleaned the throttle body etc. etc.) and it now doesnt bounce around or cut out anymore but just sometime driving its like you have someone just holding onto the car a little to stop it going quite as it should, it could be i am being very picky, my problem is i am a bit suse by the cars engien as i bought it with a rebuilt new engine with new belts etc and bout 3 months in pop belt went, i believe the engine to be a cf2 from a 147 and mine is a 99 model pre-face lift but would contain the cf2 engine, i have rebuilt and done metal conversion tot the engine to go back to alli engine. any info would be interesting to look into cause i am coming to a bit of a wall as i think everything under that bonnet is now new. and that is no exageration. and dont get me wrong the drive of it 99/100 is lovely and spot on but like i say maybe being picky just sometimes feels like weight is holding the car byu the spoiler and saying no not today you aint gonna get away, but i remember my first 145 took out the restrictor and that thing flew its was stupid fast for standard and occasionally that just didnt wanna go somedays.
i have always thought these cars are like us somedays you wake up and just cant get yourself going and then other days you fly like a plane.