I’ve got a 2001 Ford F150 with a V6. Some time ago I took it through a car wash and before I got home two codes were logged. Lean mixture both banks. I figured maybe the water got into the oxygen sensor hoo-ups. I erased the codes thinking next day no problems. Well came back and has been constant even though I reset codes one more time. Both O2 sensors bad same time ? How to determine, O2 or vacuum leak, and if the latter any tricks on hunting down a leak? All my money is going to day care for our 6 month old, AKA strapped for cash or I would have taken it to a shop.
Will it do a 0 to 70 full-throttle acceleration without any mis-fires or other problems? Did the acceleration test feel “right”?
As for guesswork, mine would be clean the MAF, change the fuel filter, add a bottle of Techron to the gas when it’s below a quarter tank, check the fuel pressure at the fuel rail test port…
Vacuum leaks usually produce a rough idle as one cylinder will be so lean it mis-fires at idle.
How about a MAF sensor cleaning? worked for me when I got a “too lean” code (P0174) on my 2004 F-150.
As oldschool notes, certainly clean the MAF first. This costs about 10 minutes of time and 15 cents worth of electronics/MAF sensor cleaner. Also clean its electrical connectors.
One simple way to check for vacuum leaks is to hook a piece of some kind of hosing to an UNLIT propane torch. With the engine idling fish the propane around the vacuum connections and intake. If you hit a leak the engine should rev up. There should be a schematic diagram of your vacuum system under the hood to help you find it all.
I would do those two things and then pull the O2 sensor wiring harnesses, clean them, and check the power supply.