My car has had a engine conversion from a 1.8 to a 2.5 m52. It's has also be turbocharged. When I start the car it fires up straight away with no hesitation but it just revs up to about 2000 rpm then down and cuts out. If I sit in the car and start it and keep giving it small amounts of revs the it will keep running but as soon as I stop doing it it just cuts out.
My car has 100000 miles.
My car has a manual transmission.
Anytime a car has been modified, it is tough to give valid advice from a keyboard. There is just no way to know what has been done. I can give you some general advice however.
I would first suspect the IAC (idle air control) valve. This valve is responsible for the idling of the motor. Is it plugged in or has one of the modifications affected its programming. Vacuum leaks are possible as well, except they will usually cause the motor to idle high non-stop.
The big one that is easily missed when modifications, such as this are done is the MAF (mass air flow) sensor. If this isn't installed in the system correctly, it will cause your symptoms and many others.
Also, a car with a turbo will need to be properly tuned to the motors intake and exhaust systems. I would first begin with connecting a scanner and reading the data. For something like this, I recommend using a German specific scanner. Snap On and other American made scanners don't have the greatest functionality when if comes to German cars. If this trouble persists, I recommend having a certified mechanic, such as one from YourMechanic, diagnose your car's stalling problem in person and let you know what should be done.
Good luck! I hope I have helped you.
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