Engine/Transmission (1998.5 - 2002) High idle, then normal idle

Hello- I have a 1998, 24 valve, 3500, 4WD, automatic, with 252,000 miles. It has a Gail Banks Stage 3 kit but otherwise stock. Truck starts fine, initially idles where it has since I bought the truck brand new. (About 850 RPM in park?) After driving for a while, come to a light or a stop sign, place the transmission in neutral, to save on the transmission, and the truck will "idle up" to about 1,000 or 1050 RPM. OAT is around 85 F plus, Air conditioning has been on and off, still does the same. NEVER had this problem before

I suspect injectors or APPS. Thoughts and thanks in advance.

Kenny

 

Sounds like something went wacky with the cold weather high idle option. Is that option enabled?

What is the coolant temp when this happens? Is the thermostat stuck open? If below 140 degrees that is one of the triggers required to activate the feather. The other is OAT sensor under the drivers battery. SnoKing