Hello, I run a 97 Civic 198,000 (KM) and the engine has a high low rev problem at idle. However it is not a cold idle, but at a warm idle. It has absolutely no effect on normal driving, just when you are sitting or hold the clutch in for a few seconds. I've heard many explanations ranging from Idle air control, to throttle position sensor, a vaccum leak, or even the timing being off. Anyone know the exact reason? I was even told to drive it for a while and see if it doesn't work itself out. There are no mods on the car. Maybe I should just hook it up to the computer? and there is no check engine light on.

 

Vacuum leak.
Dirty/sticky IACV.
Air pockets in the cooling system.

It could be one or more of these. You have to rule out each one & go from there. It's not always caused by the same thing for everybody's car.