Problems with RPM's

[cgg074]

I recently bought a new 2003 Mach 1 (Manual Transmmission). It only has 1,500 miles on it. Since I have it, I've noticed problems with the RPM's.

Sometimes the RPM's get stuck in 2,500 RPM when I'm driving. I have to accelerate or turn off the engine and start it again to get the RPM's normalized. The problem is that this happens ONLY once in a while, not all the time. The dealer said everything is allright. Obviously, the problem didn't came out when they tested it because it doesn't happen all the time.

The Check Engine DOES NOT light up when the RPMs get high.

What could it be?

-The TPS (throtle position sensor)? I believe that in the late model mustang the TPS is not adjustable. Could it be damaged? I checked it with a scanner and it said it was ok. 21.5% when not pressing the accelerator pedal.
-The Air Valve behind the throtle?


Please help me with some advice!!

Thanks,
Carlos