I have a problem with my automatic 94 Civic EX. After i drive my car for a bit and put it in park or neutral, my RPMs go up and down from about 1000-1500 RPMs.. What could it be??

 

Sounds like the map sensor to me. Do u have a cel.

 

How can you be sure? There is several things it could be.

 

Well help the op by telling him the several things it could be.

 

This happened recently after i replaced my head gasket, i did it myself but i know i did everything right and put it back together right. Someone has also told me it could be the Air Control Valve.. could that be it?

 

I have the same problem, Messing with the engine prior points to something that would have had to changed post head gasket change, I would first check vacuum lines, make sure all the clamps are snug and you put them all back on correctly.

 

Im not gonna start listing out the tons of different things it could be. Might as well send him on a wild goose chase if thats the case. You really need to either acquire a OEM service manual or download one and diagnose it yourself, or take it to a mechanic. This isnt something that can be diagnosed over a message board

 

96 and under civics have the fast idle thermo valve.


That is most likely your issue since you said it happens once it is warm..


Try bleeding your coolant system for starters.

 

-bleed coolant


-clean IACV
https://honda-tech.com/forums/acura-integra-6/%2A%2A%2Ahow-clean%2A%2A%2A-your-iacv-k-idle-air-control-valve-1575913/

-clean FITV
https://honda-tech.com/forums/acura-integra-6/%2A%2A%2A-how-%2A%2A%2A-clean-your-fitv-aka-fast-idle-thermo-valve-1564019/

 

I took off the IACV and cleaned it out, and i also bled the coolant system and it still runs the same

 

I took off the throttle body, FIACV and IACV and cleaned all of it, and it still seems to be running the same

 

Problem solved! I replaced the Idle Air Control Valve and now is running good without idle problems :D