After removing 2/3 of the wire harness of a 92 prelude, (car has been completely gutted), after warm up, the idle will start at 1800 for 2 seconds, then drop to 600 for two seconds, then cycle back to 1800 rpm. it is a smooth idle. and the variation is steady. nothing rough or erratic. setting the idle at 1700 removes this problem. the engine still revs like it should with nothing out of the ordinary.
Does anyone know of a sensor or valve that can cause this to happen?

 

I posted this from memory. I Let it warm up, then listened. I will rev to 1800, then it sounds like the spark cuts till it drops to 700 rpm. It is rythmic, and steady enough to keep time to it. No problems when the gas is applied. I took it out to a field and let it have all it could take. nothing I could feel or hear when then gas is applied affects it. It is just the idle is embarrasing when it will be staging for a race. It does show to be just a tad rich.

 

It's either a vacuum leak, the IACV, the FITV, or the throttle plate is not closing all the way....Do a search on here and you'll get way more info.

 

it was the iacv (anyway, it was unplugged). thanks alot. it is purring at 600 rpm again