Erratic Engine Idle
 

Hey guys Im new to the forum. I bought a 91 Accord EX Station Wagon at a police auction a few months ago. Put a new battery in it and it started right up. The only problem is the idle instantly shoots to 3k then drops to 1.5k then shots back up to 3k and drops. This is just constantly going on the entire time. Like a ghost is revving the car haha.

Anyways, aside from a exorcism what else could fix this?

Thanks!

Fast Idle Valve
 

Looking into engine bay . Look at intake manifold. on the right side ( drivers ) and vertical with two small coolant hoses at bottom, is the fast idle valve. This is what controls what your describing. The coolant may not be getting to it. Possible low coolant or restriction. if ok there then replace the fast idle valve.

You can also remove the cover to the fast idle valve (FITV) and tighten the plunger. There is a writeup in the DIY section about this.