98 Civic DX with 80k, and i noticed it's starting to idle high when i start it, then it takes about 5 minutes and the idle will lower. It does it all the time, but even more so when it's cold. Idk what the RPM's are b/c i don't have a TACH. I also have noticed a drop in MPG, which could be just b/c it's winter now, but maybe b/c it's Idling and revving to high? Suggestions please, thanks in advance

 

it's suppose to do that

cause: fast idle valve operating normally

It makes you idle high to warm the engine up. When the engine's coolant is at normal temp, the FITV closes and idle is normal

 

The longer time it takes for the engine to warm up in the winter will somewhat decrease mpg in the winter. If your reduction is dramatic, start by doing a basic tune-up, which is replacing the plugs, wires, distributor cap, and rotor.

 

My car has been doing this recently, except it's a little different. It hasn't been doing it consistently until last night driving back home from the movies (a longer drive, so engine should have been plenty warm). It starts up, revs to about 2-2.5k rpm, then stays at about 2, even for a good 10-15 minute drive. It's very frustrating to me, and it's been cold for a while.

Someone suggested a sticky throttle valve cable or something? Or is it the suggested thing from above