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Q: One month ago cel came on I changed spark plugs to after market plugs. One month later cel on again with misfire code.

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Cel keeps coming on. 1st dealer gets misfire codes on 3 and 4. Says could be after market plugs so changes them to. Subaru plugs. 150 miles down road cel on again. Next Subaru dealer another 650 miles road. Misfire code on 3 and 4. Couldn't find anything, drives fine, reset codes. 500 miles down road cel on again. Next Subaru dealer misfire code on 1, 3, and 4. Says valves need adjusting. Getting very frustrated with non definitive solutions which keep costing more money. I am out 360 for spark plug replacement which was obviously not needed since it did not fix the problem...

My car has 130000 miles.
My car has a manual transmission.

A: If the spark plugs hadn't been changed ...

If the spark plugs hadn't been changed until 130k, it was time for the to be replaced anyway. This is probably why the dealer went with that repair as worn spark plugs can cause misfires. Ignition coils are another part that may fail and cause misfires when they malfunction. A compression test and cylinder leak-down test will show if there is a problem with the valves. You can try having the coils replaced and the valves adjusted by the dealer. Consider hiring an experienced technician like one from YourMechanic who can come out and conduct the same tests as the dealer could and determine the cause for your check engine light.

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