Here's the problem:

When my car is cold and I turn it on, then engine revs itself up to about 1500rpm. It then starts fluctuating between 1300-1800rpm with a frequency of about 2 seconds. "vrooom.....vroom....vroom...." It does it for about 5 minutes until the engine warms and then the idle starts to come down to about 800rpm.

Whats teh problem here? It happened after I reset my ecu after doing a mod (not sure which one).

Here's another possible clue: If I tap the gas after I start the car, it behaves totally normally. If I don't touch the gas then it behaves as described above.

 

mine did that and my TPS is bad.