Recently i had a valve job done on it. They resurfaced the upper head as well. After getting everything back together, It ran. The engine light was still on, but i figured it was because i never reset it. About 800-1000 miles later I checked the codes and recieved "missing or bad o2, missing or bad MAF". I reset the ecu (A2) and drove it around, then cheked for faults in A2. I found none. When I took it in for smog I failed Hydrocarbon(max=85 meas=102) at 15mph, but passed at 25mph. I've read that O2 sensors can go bad and be undetected by the ecu. It has seemed to lose power on acceleration, but i thought maybe 'cause it had 140k mi on the engine. Should i try to clean the MAF and O2 sensors? How can I be sure they're in working order? What else should I look for?</P>


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I would try and cleaning the intake tract, throttle body with SeaFoam, checking PCV valve as well.

 

If the O2 sensor is bad, you have to replace it. There is no cleaning for that.