A friend has a 1993 Civic DX with original/stock 1.5L motor. The car gradually began to idle up, and down. It seems to rev up to 3000rpm or so, then down, etc. We checked and the vacuum lines are OK. The motor seems to be in good shape, otherwise. I am thinking it is a sensor of some kind. any suggestions would be great.....Thanx

 

I have seen cars that idle up and down in cold weather to help warm them up. Don't know if Hondas do this or not. My EG doesn't.

 

HMmm. Ya, this constantly idles up, and down even while driving.

Anyone else>??

 

If this happens during warmup and after warmup, I'd check the Fast Idle Valve, should be the little device under your throttle body. Its possible the spring is broken or something is stuck. Maybe give it a clean with some throttle body cleaner.

 

Kool! I will check the fast idle valve....anything else??