After a 4.3/5-speed swap out in the 1998 S10 it will only idle down once the wheels stop turning. The normal idle for it is about 800 which I like.

It does not matter if the truck is rolling forward or backward from a dead stop as it starts to roll the RPM's start to climb with the transmission in neutral. I can coast for 2 miles and the idle will be 1500 +/- RPM.

Everytime I make it stop it will idle down to 800 and if I take the foot off of the brake as soon as the truck starts to roll the idle speed starts to increase.

If coasting up a hill the idle will drop when it comes to a stop then start to increase when it starts to roll backwards.

Anyone ever had an engine that would not idle down if the tires were rotating? If so how did you fix it?

 

did you check the allen screw on the throttle body. there is a screw there that some mechanics turn to increase the idle to hide additional issues with the truck which are symptomatic at idle... look for it and give it a couple of turns and youll see what im talkin about