So I'm getting the 940 ready for some more boost and working through its issues and have 1 remaining issue to fix/figure out that has me stumped.

At idle the car surges from 1000 rpm 1800/1900 rpm constantly and in rapid pattern. The odd thing is that it only happens when the car comes up to operating temp (the thermostat opens and the gauge registers), when it is cold it ides high (900-1000 rpm but it is steady). So far what I have done to fix this is the following:

1. Replaced the AMM, was getting code 1-2-1 from the old one. Now no codes.
2. Replaced all the vacuum hoses with silicon vacuum hoses.
3. Removed and cleaned the IAC valve.
4. Replaced the water temp sensor for the ECU (under #3 runner).
5. Replace the intake hose between airbox and turbo, found quarter sized hole in it.

Now, after all this the problem still happens. Any suggestions? Keep in mind this only happens when the car comes up to temp.

Other info -

When I put the car in drive, it smooths out and doesn't rev/drop, its a little rough but I think that is a motor mount issue. When driving and I let off the gas ad coast it will also do the rev/drop thing.

The only thing that I can think of that is left is O2 sensor, could this cause the same kind of idle problem.

Thanks - Tim