Sometimes when I turn on my car, the idle is really high, like near 2k rpms. And even after driving for a while it stays there. What causes this? Seems to only do that during cold days, although I'm not too sure.

 

Yeah mine does that too but goes down after awhile to about 600 rpms and idles just a little bit rough. I probably just need a tune up though.

 

check your IAC valve connections, and the vacuum connections near the driver side strut tower.
im assuming you have a 4g lude.
otherwise state your specs

~boom

 

It's a 1992 Honda Prelude. Do you guys know how much it should cost to have this fixed?

 

first off
what kind of engine is in the car, they made two in 1992 :a:

before doing anything else, top off your coolant tank/radiator and then warm up the car. carefully open the bleed hole on the top of the thermostat housing, near the throttle body. bleed any air out of the system. air in that area can affect the sensor and cause erratic idle.

its most likely sensor or vacuum related so if you take it somewhere they will probably fix it in 10 minutes and rape you on price since its a lude.

~boom