The prelude im looking to buy has been sitting for about a year and the engine revs up and down to about 4000 rpm, is this because the engine is cold and its been sitting for a while...or is this something more. also its got 270000km on it..is there anything else to know about 91 preludes at this kms? thanx.

 

bump

 

sounds like it has a bad Idle control valve or something

 

Could be any one of these things:
1. Ile control valve
2. CTS=coolant temp sensor
3. TPS=throttle postion sensor
4. ECU

 

OR your PCV vavle.

a hose could be disconnected on your curise controll or TB.

many things can make an idle jump. take to a mech and make sure its not something big.