Advance ran the code and came up the "Manufacturer Contrl. Fuel Air Metering".

I have found that this code is Ford specific so I looked it up and found:
P1131 Lack Of HO2S1 Switches, Lean (Bank 1, Sensor 1)

Do I have a bad oxygen sensor or is it something related to the MAFS? I changed the MAFS a couple months ago since the old one pretty much died.

Anyone know what I should do?

Thanks in advance.

 

It could very well be a bad O2 sensor, or as simple as the PCV Valve or its grommet failed. Could also be a bad PCV hose. You also can't rule out a vacuum leak, but I have trouble rationalizing why only Bank one would detect it and not Bank two, unless it's leaking from the PCV (rear of Driver side valve cover).

This particular problem MIGHT cause me to go to the Ford dealer and pay to have them look at the data live. But, I'd PROBABLY replace that one O2 sensor first, just because I can't fathom breaking my years-long avoidance of darkening the dealer's doorway, and my wallet always feels better paying for a part that I replace rather than paying the dealer to "diagnose".

Since nobody else is replying, inspect/replace the PCV first, reset the codes and hope for a cheap fix (as in not buying an O2 sensor). Last thought is the intake manifold leaking vacuum, but again, why is it only detected on THAT side?

You can use carb and choke cleaner to find a vacuum leak. Just spray it around the suspected leak area and listen for the idle to change.

You don't mention any symptoms other than the CEL and code. High idle, low idle, hunting idle, rouns rough, misfires, poor gas mileage, etc.

If you've owned this truck since new and never replaced an O2 sensor, it's overdue for both upstream sensors anyway. But I'd sure look hard at the PCV system and intake first, money-wise.

If it's the MAF, you can sometimes confirm that by running it with the MAF disconnected. If the symptoms improve, bad MAF. If you have an oiled air filter element (K&N, etc.), it may have contaminated the MAF. Clean the element with electrical tuner cleaner, NOT carb/choke or brake cleaner. I'd also make sure ALL the connections on the intake tube are tight (another vacuum leak point). That hose in the middle is from the PCV.

 

well the cel went off yesterday, all i did was disconnect the maf and reconnect it. It has been driven at least 3hrs since then and the light has not come back on.

Thanks for the info, im sure my oxygen sensors are overdue.