20145.oh

So a while back actually a year ago my old 01 f150 4.2 would do this weird thing where sometimes when I started it up after running for a short period of time like 20 minutes it would run rough and stall out and it would do it like 3 times in a row then run like brand new no codes or anything it confused me so much I asked so many people what was wrong with it and no-one could figure it out let me remind you it was random so not every day just sometimes so I decided to run sea foam through it it has 115xxx miles on it after I did that it never did that ever again so if anyone is ever having a rough idle problem then try sea foam through it the motor could just be dirty

F150_NAMED_CLIFFORD

im having the same problem, except mine does throw the codes p0174 p0171 ive only applied sea foam through the gas tank, but thats it.

Tackle

Have you replaced the intake gasket? That is a common reason for those codes on a 4.2...

F150_NAMED_CLIFFORD

no i haven't but i did the "leak test" and never got a spike in idle. but thats on my to do list though.

Mario01XLT

You're probably never going to pick it up like that cuz odds are its the intake isolator bolts that are inside the manifold. Do a smoke test with a cigar, compressor, a can and two hoses. Works like a charm man. I struggled for a long time with those codes.
If you do decide to change the manifold gasket, just make sure YOU REPLACE the bolts man cuz those are made out of like some rubber too that mess up with time and heat. I learned that the hard way and had to take everything apart again, and that wasn't fun.

Mario01XLT

Removal of intake manifold isolator bolt assembli…:
Checking for vacuum leaks using home made smoke p…:

F150_NAMED_CLIFFORD

Im not sure if im knowledgeable enough to attempt the replacement of the gaskets myself. i just need to watch youtube videos and eventually get it done.

LiftedsKRew

I just cleared those codes, p 0171,0174, on my 99 4.2. Before you tear into anything, check your PCV valve and the hoses connecting it to the intake manifold. There's a rubber elbow right under the throttle body that could be leaking and another rubber u shaped hose at the back of the intake on the passenger side. I replaced both of those and codes were gone. Cheap fix if that solves it.

F150_NAMED_CLIFFORD

ive already replaced that pcv hose, even before the codes started