Hello everyone! As my name says, I am a noob mechanic but don't have the funds to take my truck to a shop so trying to get this solved on my own. Last year, I started having a problem where when the temp dropped below 50 degrees outside, my F150 would idle really rough and sometimes stall out. The CEL came on and reported some codes that I don't remember but pointed to bad air/fuel mix. I consulted a friend and he suggested changing out the IAC. I did that just towards the end of the cold weather spell we were having and the engine ran great so I assumed it was fixed.

Well, the temps have been below 50 for 8 days now and ever since the temps dropped the problem has come back. I took it to AutoZone to have the codes read and they gave me the following:

P1151 - Lack of O2 switches -bank 2 sensor 1 : ECM could not adjust fuel trim because of a lean or rich condition

AND

P0171 - Fuel trim bank one condition : The powertrain control module uses the oxygen sensor to calculate the Air/Fuel ratio of the engine. The computer recognized a rich or lean condition on one engine bank only.

Both printouts that they gave me mentioned the following:

Poor fuel pressur
Bad or Malfunctioning MAF sensor - Dirty/defective
Oxygen sensor defective
Fuel injector problem - Leaking or fuel pressure high/low
Vacuum leak on engine


I again called my mechanic friend and he suggested cleaning the MAF and if that didn't work replacing the MAF. I cleaned it and the problem was better but still not fixed. Before I go buy a $100 MAF sensor, I wanted to check with the experts here to get some advice or opinions on what might be the problem.

Thank you for your time!

 

Codes 1151 ad 171 are for each bank so both are seeing the same fault but reporting it with different codes. Look at the descriptions again.
You have an air leak at some point in the intake tract.
Inspect every rubber item for softness, crack and rot and intake hose for being fully in place.
The reason you have stalling and rough idle on cold starts is the fuel tables are out of limits and cannot supply enough fuel for the added air leakage.
A look with a Scanner at those tables would verify it.
.
Normally a cold start richens up the fuel, opens the IAC and advances the ignition timing.
With this series already out of balance you will have an issue.
.
After finding the problem you should reboot the computer back to it's basic table configurations and do a fast relearn.
To do this you would start a cold motor, let it fully heat, drive about 5 miles do several hot restarts and return to allow the alternator to recharge the battery and present it's load on a hot motor as opposed to a cold motor.. The program keep track of hot and cold start requirements.
This will allow very good cold starting and continued relearning over several more drive cycles as long as there are no other issues.
.
At this point, now, you have no idea how sensitive the program is in running every part of the system.
One fault and it's out of full control.
This is why it set codes to tell you is needs attention and has poor drivability.
Good luck.

 

Thank you for helping me out with this. I will check all the hoses, clamps, etc. this weekend to see if I can find the culprit. I'll post back if I am able to uncover what the issue is and if your suggestions have resolved it.

 

Look above the drivers side valve cover toward the back. There are two small vacuum hoses abou t1/4 inch ID and 8 inches long. Lay real close to the EGR tube and can get hot / dry/ crack. I had that a couple years ago on my 2001. Look at all other vacuum hoses also. Maybe pull them off and look for brittle / hard/ cracked