With these codes listed, what should I change first?
I now have some codes from the car in question; 1. P0136- We replaced the bank 1 sensor 2, it helped slightly. Also the car has 155000+ miles 2. P1131 3. P1151 4. P0300
what do all the codes mean?
P0136 is the O2 sensor that you replaced. P1131 is Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1 ---- P1151 is Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2---- P0300 is Random/Multiple Cylinder Misfire Detected < - not surprising with the O2 codes.... I don't know what you should change first but I'm seeing a lean condition on your O2 sensors. I would check the fuel pressure to the fuel rails. A low pressure would make it run lean. The O2 sensors are doing their job and I don't think that they all failed at the same time. Look for causes of the lean condition ie worn fuel pump, clogged filter, bad fuel pressure regulator, etc. Good luck.
A vacuum leak is the most common cause for a lean concern check all the vacuum lines on the motor. All the concerns tenspeed listed are also valid.
We cleaned the mass air flow sensor, and the cold start problem was resolved, thanks for all the suggestions
cleaning the MAF only helped for a day, since then we replaced it
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