Truck Repair: Fast Idle on 1999 Explorer, throttle position sensor, air control valve

Question
Hi,
I have a 1999 Ford Explorer with a 4.0L SOHV Six Cylinder with an Automatic Transmission.

Lately, the idle has become fast around 1000 RPM's & when the AC comes on, it will go on up to 1600 to 1950 RPM.

The check engine light Does Not Come on either. Any ideas?

Thanks for your help,
Jeff

Answer
Hi Jeff,
I hate to leave you with that non-answer.
I can suggest that you check all the vacuum leak possibilities...hoses, brake booster, a/c controls, and make sure the EGR valve is closing.
Then, the idle air control valve can be cleaned.
All of thease are cheap, and do-able at home, without special equipment.
Throttle position sensor, or a couple other sensors could cause the idle to speed up, but without a manual, and testing them, I sure recommend that you don't just start buying parts and replacing them...gets expensive.
A scan tool connected can read the sensors real-time, and that could really help.
Van