I have a 2003 3.0 151,000 miles with CEL and codes P0172 and P0175, (rich on both banks) with a rough idle and intermittent stalling when coming to a stop after the truck is warm.
My scan tool shows long term fuel trim maxxed out Negative on both banks attempting to lean it out, and the exhaust also smells rich. I have been chasing this rough idle for a little over a year, and finally took it to my local ford dealership for diagnosis. They had it for 3 days, and came to the conclusion that i had an exhaust valve leak on cylinders 4 and 6, and recommended 2 new cylinder heads (for $4,000 with labor).

My questions:
Cylinders 4 and 6 are on the same bank. Could an exhaust valve leak bad enough that it affects the upstream O2 sensor on the opposite bank? I'm skeptical about that.
If the exhaust valves were the issue, would it be intermittent? My sluggish/stalling symptoms are nearly impossible to repeat in any configuration and seem very intermittent.


Things I've done:
Checked fuel pressure (55psi)
Smoke test for vaccuum leaks
Sea foam air intake treatment
Sea foam fuel treatment
Checked and cleaned all grounding wires i could find

Components I've replaced:
O2 sensors (upstream L and R)
MAF
Coolant temp sensor
Idle Air Control
Throttle Position Sensor
PCV Valve
Fuel Pump
Fuel filter
Fuel rail pressure dampener
Injectors
Crankshaft Position Sensor
Camshaft position sensor
Canister Purge Valve

I'm out of sensors to replace, and out of ideas of what to troubleshoot next. Any advice or experience with these issues is welcome. Thanks!

 

Tanner, I have the EXACT same issue with my 2003 and have changed many of the same components. Have you figured anything else out? I'm at a loss and it drives great other than the occasional "almost stall at a stop light when warm."

 

to answer both of you questions I'd do a compression test. that way you will know if your valves are good or bad... you can get remanufactured heads for $400 and up.