Hi folks,

So I've got a 2000 Ranger with 158k on it, rebuilt '06 engine with 65k. Been throwing an O2 sensor code for awhile now, have tried replacing all O2 sensors (done last fall), just recently replaced the mass airflow sensor as it was throwing bank 1 and bank 2 fuel lean codes (forget the exact codes now) and that fixed those codes, but the O2 sensor code P0153 Bank 2 Sensor 1 is still coming back on. The engine is kicking/missfiring pretty noticeably over 65mph. We replaced all spark plugs last summer, could the faulty MAF have caused them to be fouled up already? Or could there possibly be another cause for the missfire at higher speeds? We've considered getting the timing belt replaced, but the rebuilt engine was put in in 2008 and I would think that would have been done then... but I honestly don't know.

I saw on another post here that a faulty thermostat was causing the O2 sensor code, just a few days ago I was running Max A/C and noticed suddenly that it quit blowing cold and the temp was rising, switched to heat and temp went back to normal, and then when I went back to A/C again, it was going just fine.

I really want to get rid of this missfire as I'm hoping to sell the vehicle asap.

Thanks for any suggestions!