I have a 2002, F-150, 4x4 with the 4.6l engine. When I start the engine, it begins to surge and the rpm will not hold steady. It will increase to 900 - 1000 rpm and then decrease to 300 to 400 rpm. It also will sometimes shut off. I removed the IAC and cleaned it thoroughly. Still didn't solve the problem, so I purchased a new unit and there was no change. I have replaced 7 of the 8 COP's and have a good feel for when they are bad. This problem is different. When the throttle is increased, the engine is smooth. I have searched the forum for ideas, and see some posts related to cleaning the MAF unit and general cleaning of the throttle body. I'll try that this evening and look for vacuum leaks.
The CEL is illuminated and the codes are multiple; Oxygen sensors, right and left banks lean, High voltage on DPST; Low voltage on DPST. I will clear them first and try the cleanings suggested.
Any other suggestions/ideas?
Thanks

 

Looks like you need o2 sensors and new DPST

BTW- is your IAC motorcraft or aftermarket? my past experience has led me to believe the aftermarket IACs are JUNK and the motorcraft units are the only one's worth a darn

 

First, I apologize to the forum for not responding quickly after correcting the problem. The cause of the problem was a collapsed and leaking elbow in the vacuum line on the firewall side of the throttle body. It was almost impossible to see without removing the throttle body, EGR valve and related components. Had to purchase a complete vacuum line assembly from Ford to get the elbow I needed. Installed the elbow and the problem was solved.
Thanks for your input!