engine running too fast

I have the same problem in my 2001 blazer 2wd 5 speed manual (83,000 mi). After cruise of about 20 minutes or more, the engine revs to around 3000 rpm in neutral for a few seconds, then returns to normal idle. When still on the highway, it will actually accelerate the car if in a low enough gear. Worked the throttle cable and didnt find any sticking.

Not sure if you're still looking for an answer to your problem, but i removed and cleaned the mass airflow sensor (between the air filter box and intake), disassembled it and cleaned the sensors with quick drying electronic contact cleaner. fixed the problem. most places say that you need to replace this part if it is dirty because the autoclean cycle isnt working properly, and eventually im sure it would need to get replaced, but a five dollar can of cleaner is better than a hundred dollar sensor that isnt totally necessary.

I've also been told to check the idle air control valve for deposits. And that it can be fixed by running an injection system cleaning machine on it. It costs $ 140.00 so I haven't done that yet. I'll try the mass air flow sensor first, thanks.