Let the pending codes go - Fords in particular like to keep a list of pending codes that often never see the light of day. Some Toyotas are good at that too, but you have a Ford.

P0135 says the heater circuit in the forward O2 sensor in bank 1 (passenger side) is not drawing current. The fault is rarely in the sensor but a mechanic needs to troubleshoot it. You could spend a small fortune guessing. However, that code won't hurt anything but emissions during warmup.

P0171 is saying the mixture is too lean on bank 1 (passenger side again). Sounds like a coincidence that both are on the same side. The most likely cause of P0171 in Fords of that era is a vacuum leak... again, something a mechanic should find quickly. A torn PCV hose is a common cause but you really will be money ahead to have a pro look at those issues.

The last one could be you just left off the gas cap. The first one you can change to O2 sensor and clear the codes and see which one comes back on. The lean one means it is not getting enough gas so that is sensor (always sensor first) then pump not providing enough pressure, maybe a clogged filter. Change gas filter it is cheap and easy, clear codes and see what comes back on. That is what I would do.

GL

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