I’m a mechanic but this problem has me stumped. I recently replaced the radiator 2 weeks ago because it developed a leak and ever since then the truck won’t go into decel fuel mode when you let off the throttle. I’ve replaced the iac and relearned, checked tps it reads 0% with throttle released and 100% at wot. I have also removed and cleaned throttle body and checked for vacuum leaks, sprayed all around intake and throttle body with carb cleaner. I have a snap on scanner and looked at all the live data and everything looks fine as far as maf sensor, iac, tps, and ect. Truck idles fine and runs great just can’t seem to figure this problem out any help would be greatly appreciated.

 

Is this a constant problem or does it only occur after the truck has been driven and/or engine is up to temperature?

What is the IAC count position when the problem is present? If it’s at the zero count position, the problem is being caused by something that’s outside the range of IAC adjustment (stuck throttle or vacuum leak).

What are the TPS voltage readings? It should be 0.6 at idle and 4 - 4.5 at WOT.