So I had a problem with my check engine light coming on, so I pulled the code, it said it was a Coolant temp sensor. Easy enough, went and bought a new one, threw it in there, no more check engine light. However, while I was driving to the store for the part, I ran into another problem. When I put in the clutch, my RPM's jumped to around 3000. So I push the gas to make them drop, and they do, but after they drop to idle, it was pulsing up to 2000, then back down to 800, and so forth. It either stays at 2500, or pulsing between 800 and 2000. I'm thinking it's the aic valve, but I'm not sure. I talked to some people, and they don't seem to go up very often. Anyone have any good ideas on where to look at?

Edit: It's a 1994 Prelude with a H22A1

 

you have a vacuum leak. Check all of your vacuum lines and make sure everything is attached in their appropriate places. If its not the hoses leaking, your gonna have to do some searching around the intake side of the head until you find it. Start at the head where the manifold bolts to, then go from there.

 

I can't find the write up.

1. Unbolt your IACV from the throttle body. 2. Take the inspection (metal plate with i think 3 screws off. 3. You will see a big plastic white thing with threads on it. (sorry i dont know what you would call that ) 3. Take a screw driver and place it into one of the little slots in the top of the big white plastic thing with threads and screw it down until it bottoms out (screw all the way down and stops). This piece im talking about will back out over time and cause your car to do what you are describing. You can also pull your intake off and look into the throttle body and you will see a small hole stick your finger over that and see if your idle stops surging. If it does then i know this is your problem.

 

heres a how to http://92lude.com/idle_air_control_bypass_mod.htm
clean it also with carburateur cleaner and is should be working fine after that!

 

I'm going to check it out tomorrow, thanks for you help guys