My 2000 Explorer check engine light came on. One code- P171. I cleared the code and 2 weeks later came back with P171 only. Car has 98,000 miles. About 4,000 miles ago, I installed the upgraded timing chain tensioner kit so I had to do the upper intake gaskets. I did the plugs at this time. I just bought a large can of carb cleaner and sprayed all over the upper and lower intake gaskets while running and had no change in rpm's. I also sprayed by all vacuum lines and got no change. I'm thinking it's the o2 sensor, I bet they are original. Which o2 sensor is bank 1? Should I check anything else before buying the o2 sensor? Should I replace both o2 sensors at same time? I'm assuming there's only 2 o2 sensors. Thanks for any help.

 

Visually check again for any and all air intake related connections from the MAF sensor back.

What size engine do you have?

When using the carb cleaner method of locating an air leak can be tricky. Sometimes the engine will "rev up" only

a few RPMs and may go undetected while your head and ears are in the engine compartment.

 

4.0 SOHC. I checked all vacuum lines. All hoses in good shape.

 

doing a search of code, it's hard to figure out where to start. could be fuel filter, dirty mass air flow, pcv, O2 sensor. I'm thinking a dirty mass air flow, clogged fuel filter or bad pcv would throw codes for both banks P171 and P174. Is that right?