Greeting fellow Dakota fans! I have a 3.9 that is surging and dropping off at idle. At idle it seems like some cyl's are shutting off, idle speed drops to below 600 and is rough. Then it smooths out and speeds back up to normal. There are no codes set, no check engine light. The truck has new plugs, wires, rotor and cap a month ago.

Any thoughts ??

Jon

 

Idle Air Control (IAC). It is located on the back of the throttle body. You can remove it and clean it up, use a shop rag soaked in TB cleaner and gently clean the crusty crud off the pintle end. Put a little 3 in 1 oil around the pintle shaft bore to lube it but do not push the shaft in and out of the motor housing, that can ruin the stepper motor. Clean the IAC orifice on the TB too and lube the o-ring with clean motor oil before reinstalling it. It is best to remove the TB so you can clean it also. Be sure to remove the MAP and TPS sensors before you spray TB cleaner on the TB. If cleaning the IAC does not help you may need a new one. If the pintle is fully extended when you remove it from the TB that may be a sign you have a bad IAC.

Jimmy

 

I will give it a try. Thanks Jimmy!