Car problem question:

I scanned my 2002 Taurus 3.0L for codes because of engine erratic idle, misfiring and hesitation. There was no codes but my long term fuel trim (LTFT and Short Term Fuel Trim (STFT) are over the limits (should be +10 or -10) when I rev the engine up. My cousin who owns the car has just changed the head gaskets including all the tune up parts like plugs and wires. It was doing the same after all these repairs and the fuel trims are still out of range (+ 24). How do I fix this?

ATS Adviser: Watch your oxygen sensor live data and find out which one has the high STFT after you got the engine warmed up. (In your scanner live stream, you can set it so you can watch both fuel trim and 02 sensor readings monitored at the same time). You have 4 oxygen sensors on this engine. Once you replaced the one with a high reading, it will return to normal which is between 10 to -10.


My original STFT reading for the left front bank oxygen sensor was over 20. After I replaced the sensor, went back to +2 and -2. Now the engine runs perfect! The idle is smooth and all sensor reading like TPS and DPFE are all normal. Thanks!

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