Q: What repairs fix codes P0172 and P0304? I just had all the spark plugs replaced recently.

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My check engine light has been on for about a month now. The vehicle seems to stall and feels like the engine loses energy sometimes or wanting to come to a stop. I had the check engine light checked and got codes P0172 and P0304 and was told to replace ignition coil for cylinder 4 and that spark plug. I just had all four spark plugs changed so is it necessary to replace that one as well? And should i replace all the ignition coils or just that one? Also what codes fix this if not the ignition coils?

My car has 150000 miles.
My car has an automatic transmission.

The P0304 code indicates a misfire has been detected on cylinder 4. The P0172 code indicates that the fuel mixture is richer than the mixture control can compensate for. It’s possible that they are related, but not necessarily. Rich mixture can be caused by excessive fuel pressure, or sometimes by leakage at a fuel injector. If your misfire is caused by leakage at injector number four, then it’s likely that the two codes have a common cause. It’s also possible that you have had a spark plug foul because of a rich mixture. Again, that would be a common cause. But it is also possible that you have a failure in the number four ignition coil, they are not uncommon. In that case, the P0172 would be a separate issue altogether. If I were working on the car, I would try to determine the cause of the over rich mixture and then work from there. In any case, you need to have a qualified technician check this thing out. Contact Your Mechanic and they can send a technician to your home or office to check out your car and tell you what needs to be done.

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