Intermittent high idle is a common problem. There are electrical wiring harness issues to the TPS (Throttle Position Sensor), IAC (Idle Air Control) valve, and Mass Airflow Sensor (MAF). The issue is not the sensors themselves. It is the electrical connectors TO the sensors. They develop corrosion and high resistance over time. The result is random CEL's (check engine lights) and the most common symptom where the engine idle suddenly and without warning jumps up to 1500 RPM or above.

The fix: There are two fixes. Fix 1: Unplug the connectors and clean them up as best you can and re-crimp them. You should be good to go...at least for a while. The problem will eventually come back. Fix 2: Unplug the electrical connectors and cut them off. Solder the wires directly to the TPS, IAC, and MAF. Yes, this is a drastic move. But guess what? It fixes the problem PERMANENTLY. I've done this on my Sportage and haven't had any wacko idle problems since.

The TPS is located on the throttle body where the aluminum intake bolts to it. The IAC is on that same intake roughly above the exhaust side of the engine. It has a connector that faces straight up. The MAF is between the air filter and rubber flex pipe up to the intake. The round plastic unit with an electrical connector on the backside.


Also, one other item to check. Make sure the ground wire between the battery tray and the intake manifold is corrosion free and tightly connected.