I have a 95 Honda civic. It started revving up and down constantly a few weeks ago. It goes up to about 3000rpm and down to 1500rpm over and over. I replaced the IACV but it didn't fix the issue. Anyone else have a suggestion ?

 

i really don't have that much experience with anything bigger than a briggs and stratton but occasionally we get a lawnmower that comes through with the same problem and its usually the throttle spring has come loose and is letting the throttle wander back and forth due to vibration

 

Take off your intake pipe. With the engine running, plug the bottom hole in your throttle body. If it brings your idle back to normal than your "Fast Idle Valve" needs to be tightened up!

If this works than post back here and i'll try to find the write up with pics on how to fix this.

 

^better answer

 

i had this problem as well. i went through my IACV and my FITV, and cleaned both and readjusted the Fit valve. still had the problem. so after hours of forum searching, i came across this thread: http://www.superhonda.com/forum/f55/...oblems-259965/ (i know its not HT, but its FULLLLL of great info and pics) in the end, it ended up being a bad TB base gasket. i just put the new one on today, and my idle surging went away completely! also, her is another great write up: https://honda-tech.com/forums/acura-integra-6/%2A%2A%2A-how-%2A%2A%2A-clean-your-fitv-aka-fast-idle-thermo-valve-1564019/

 

PLUG THE BOTTOM HOLE!!!
1st; Unscrew intake pipe
2nd; pull intake pipe away from throttle body.
3rd; start engine
4th; plug hole with your finger and observe if this fixes idle issue

Don't listen to guy above me, until first trying this. It should take no more than 10mins and will answer alot of questions!!