hello everybody,
i write from italy so sorry for my english
i have a Ford ranger xlt 4.0 1997 v6.
i have p0171 p0174 obd error.
i repleaced:
maf sensor
Head gasket
idle valve.

problem:
when it run hot, in P idle is rough and go up and down.

what could it be?

thanks to everyone
michele

 

It could be a bunch of things: https://www.obd-codes.com/p0171

PCV valve/tubing, O2 sensors, sticking/plugged/failed fuel injectors, or a vacuum leak somewhere. If you can run a smoke test, that's a reasonably straight forward way to find a leak.

 

I know you have the two lean codes now, but what codes or issues did you have before all the work was done?

Or was this work done trying to solve the two codes?

Plus one it is very likely to be a vacuum leak, I would suspect the intake gasket or a central vacuum line that would effect both banks.

Cool dog by the way.

 

In the last rime i repleaced both head.
Maf new
Iac new
Spark plug new
Spark plug wire new
Coli new
I think the PVC tube, the 3 small tube but i don't know.
The truck run perfect but in P or N or when i don't accelerate the idle is rough and stall.

 

If you have looked over the engine and do not see or hear any obvious vacuum leaks, you can use a small propane bottle with a regulator and hose attachment to pin point a possible leak.

You could also use carburetor cleaner or other flammable spray cans to do the same thing but if you get it too saturated and encounter a arc from the ignition or hot manifold you could have a fire on your hands.

For safety reasons I prefer using propane.

The best way to locate a leak to to take it to a shop and have them do a smoke test on it.