I have a 2001 F150 5.4L with 128K. I've been experiencing the classic rough idle, stalling, surging. I get both PO171 and PO174 codes, never just one.

I've read various threads on this forum, great info. I've replaced the PCV and air filter. I've cleaned the MAS. But still did the surging all last week. This morning I proceeded to see if there was a vacuum leak. I've sprayed carb cleaner around various vacuum points. Doesn't seem to make a difference.

For the last hour its idled fine both in neutral and in gear with my foot on the brake. What the...

What is the chance the extremely cold air temp will affect it. The last week has been high in the teens with a subzero chill factor.

confused

 

Possibly a failing IAC valve. Fairly common for Ford's in general.

 

If it stalls, then starts right back up, chances are it's the IAC valve. With that many miles and you've never replaced it, it's time for it to go out. If so, don't clean it --- replace it. It'll just act up on you again no matter how clean you think you got it.

 

Thanks. That was going to be the 3rd in the process. I guess I'll make it the 2d.

 

Have you followed the hose from the PCV valve to the back of the intake manifold, under the throttle body? The rubber elbow back there is a high failure item and will throw lean codes.

 

Replaced the IAC. The forward end of the chamber was coked up. I bought an elbow from Autozone that they said would fit in lieu of the MFG elbow - not even close. Even though, the MFG elbow was still pliable, not brittle or weathered. For now I'll run it a couple of days and see what happens.