I have a 1993 Honda Prelude with an H23 and a 5-speed. I've been having a problem with a the idle jumping for about 2 months now. It'll go from about 1500 to 2100 after about 3 minutes from startup and continue pretty much the entire time I'm driving it whenever the clutch is pushed down or it's in neutral. The car doesn't run any differently when it's moving and you're on the throttle. When you're in gear and off the gas, it'll sort of drive itself if the idle has been jumping. The only mods are an AEM cold air intake, K&N Cone Filter and a catback exhaust. I have no check engine light.
I've already taken off and cleaned my IACV and that kinda helped it for a day. I took it to the local mechanic when it started surging again like a mad man. He charged me for one hour of labor saying it was a ground wire to the IACV. It idled really low like 500 rpm and was close to stalling after he "worked" on it. Then my car started surging again 2 hours after leaving. Same problem. Nothing fixed.
I know I could bleed air from the coolant, but my buddy said that if the car isn't overheating, then there isn't air in the system. It rarely heats up to halfway and goes back down really fast. Someone told me to replace the spark plugs. I did. Made the motor run "smoother", but still surge...
If I have been driving for a prolonged period of time, the jump will stop, or drop to about 1000-1400.
There's two vacuum lines on the throttle body. Here's a pic I got off Google (not my engine and you can't exactly see where the lines are, but the general area)
#2 doesn't go anywhere. The line looks like it was cut off. If you disconnect #1 when it's surging, it'll stop surging, but the idle becomes very rough. I'll try to get a better picture later of my engine bay and actual vacuum lines I am referring to.
I keep hearing vacuum leak, or even exhaust leak from everyone I ask. I'm new to Honda cars and so far I've found a laundry list of problems that could cause this from doing Google and forum searches, so I'm sorry if this has been asked before and numerous times. I just need someone point me in the right direction. Thanks in advance.