Q: P0302 2003 Pontiac Aztek

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The car has code po302, misfire in cylinder 2. The vehicle recently had a major tuneup, and we checked the following:

  1. plugs
  2. wires
  3. ignition coils
  4. cylinder compression- is 130 PSI
  5. We replaced the fuel injector for cylinder 2
  6. we changed the gas filter which had nothing to do with it anyway.
  7. used two bottles of lucas fuel injector cleaner. one bottle per full tank of gas.

It is an intermittent misfire. The car seems to run a little rougher when cold, and warming up. if you jump on it from a dead stop, it will misfire almost all the time. The check engine light comes on and is flashing. It then goes off. if you reset the code, the check engine light comes back on about a week later and shows the same code again. I just drove the car 75 miles on the freeway, It seemed to not be misfiring on the freeway, then i noticed it at higher speeds 50-65 mph or around there. it then rides normal at high speeds of 70-75 mph.Vehicle computer may adjust to problem?

My car has 108000 miles.
My car has an automatic transmission.

Hi there - if I’m reading your notes correctly, you "checked" the plugs and wires, but did not replace them. For your mileage, you need to replace the spark plugs at least, and possibly the plug wires as well. Misfiring under load is a primary symptom of weak ignition components. I recommend spark plug replacement performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, replace the plugs, and get you back on the road smoothly again.

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