I have a 1989 Mustang GT. It is mostly all original, but lately it has been having a RPM problem. I will start the car and it will read at 1200 and stay there, sometimes it will even read at 2200 and stay there. It will proceed to doing this while driving. But sometimes if you let it idle for a while it will start idol normally but then if you go and hit the gas it will get stuck at over 2000 RPM again. I have replaced the EGR valve and have cleaned and then replaced the mass airflow sensor and neither of them made a difference. I'm going to replace the fuel filter but I do not think that's it. My only two guesses could be that it is a very dirty throttlebody or a camshaft sensor. Just looking for some suggestions or personal experience to solve my problem