I have a 04 f150 that has started to idle at 1200-1500 rpms when it starts up for about 20-30 seconds then die back down to 800 rpms. Only to jump back up to 1200 for a second when put in gear. Does anyone know what would cause this? At first I thought it was just because the engine was cold, but it will do it when the whether the temp outside is 40 degrees or 80 degrees. It doesnt always do it but most of the time it does it when it has sat over night. Also after it does it, the engine well act like its running rough.

 

In general with EFI your TB incorporates a throttle position sensor to provide a signal to the ECM and a start solenoid valve to provide extra fuel for starting. This would be similar to a choke on older carburated issues. This should mainly occur during a "cold start" which seems to go hand in hand with what your truck is doing, however 1500rpm seems to be a bit high, maybe a sensor going out???

 

Maybe this gives you an idea of the idle.... mine is the same way but i dont think its all the way up too 1500 RPMs i havent looked at it before but very well could be.. Mine is roughly 20 seconds as well and you can tell its sunny out and prob around the 80s and its not different then in the winter here at Ft Hood....


http://www.youtube.com/watch?v=uCAD5ORfRa8

 

Mine never breaks 1300 on an overnight cold start up.

 

Same here, the colder it is the longer it stays at 1200-1300 before it drops to 800

 

Im pretty sure mine is going @ or above 1500 rmps. I sat in my dads this morning and his only tacked around 1100 when I started it, while mine was almost up around 1500 at with 60 degrees. Also when it is cold outside, when I start it and let it idle down then shift into gear the rpms will jump back to 1500 for a second or two.