3.0 cold engine idle...

[flyin-lowe]

My 17 year old son has a 2004 3.0 with around 120K miles on it. He called me outside a month or two ago when he started it and the RPMS shot way up. He is a new driver and said it sounded like the gas pedal was stuck so he shut it off. I popped the hood and had him re start it and it was high but not super high, it was idling around 3K RPMS. After 30 seconds or so it began to slow down. Haven't had an issue since but today I drove it and noted when I started it up it idled around 2200 rpms for about 30 seconds then over the next minute or so it go back down to the normal 1K RPMs. Today the temps outside were in the high 50's so assuming there is something in the system that causes it to idle higher in cold temps, it should have been effected when it's this warm. This is our first Ranger so I don't know a lot about the little quirks, is there a throttle positioning sensor or something, or anytihng else that could be going bad? It has not thrown a code.

 

[Curious Hound]

It should idle near 1,000rpm until it warms up. At that point, the ecu goes into closed loop operation and pays attention to more sensors. It should drop to about 700rpm for normal warm idle. These numbers may be slightly higher with automatic transmission. At idle, the throttle should be closed. There is another valve called the Idle Air Control valve (IAC) that bypasses the throttle to control idle speed. First thing I would do is inspect the IAC and make sure it is clean and not sticking open. While you're there, clean and inspect the throttle. Also check throttle cable, linkage and pedal to make sure it all moves freely and isn't getting hung up on anything.

High idle can also be caused by vacuum leaks. Check all vacuum hoses and fittings for cracks, holes or disconnected components.