I have a 98 UK turbo, terzo edition... I recently(2000 miles) had a full bottom end rebuild costing 2k....
Soon after I had the rebuild, the MAF sensor failed(the bit that connects to the air filter I think), so I splashed out £300 for a new one.
The car has been running sweet, up until yesterday, when it started to drop in revs whenever the car was stationary, at lights or in traffic. It only seems to happen once the car has warmed up, and sometimes it will only occur if I rev the car while in nuetral..It will keep happening evry time the car stops. The only thing that stops it, is if I hold down the left and right front window switches, this brings the revs up, then down again, where they stay.
The car idles between 300-1100rpm at worst, jumping up and down like a yo-yo....

Does any one have any idea what it could be, or how to fix it?????

Thanks for looking

 

Sounds like you might have a vaccum pipe off somewhere causing an air leak
on the Induction side.