The idle speed (RPM Gauge) goes up and down

I would assume that you have already check for vacuum leaks. There are a couple of vacuum hoses that are soft and become rupture over time. if all looks Ok, it is best that you bring it to the shop. 818 701 4061

Sorry, I wanted to see the answer, not provide an answer. But I could say that I had this same problem on my '97 Chevy Lumina and the problem WAS the idle air control valve. And I didn't have to replace it to fix the problem, just cleaned it up and made it move freely again. It was sticking, as I recall. This one doesn't seem to be sticking, so I'm trying to find out how it works and how to test it. Appears to be a normally open valve and I'm guessing that the closing action is just a solenoid that pushes the valve closed against the return force of the spring. I'm guessing that the computer varies the duty cycle to vary the amount of time the valve is open vs. closed. Does anyone reading this know if that's correct and/or what the activation voltage is (my guess is 5V, maybe full battery voltage, but it could be some other value in between)?

i replece the idle control cencer but it rpm is at 3 i have to wate untill it gose down before i can move i was told it is a idle speed control whats that i have a 1994 mercury rracer 1.9 4 cyl