Doing some work on this 02 WRX that was brought to me last week. They stated that the plugs had not been changed since 55k and the odometer has 166k on it so I told them they needed to be changed. I look up the OEM NGK plug and get 4 of them from advance auto.
Firday evening, I change the plugs on cylinders. Started it up and it sat and idled just fine in the driveway for 15 minutes while I put my tools up and went in for the night. Today, I changed the plugs on 2 & 4 and re-oiled the filter element on the SPT intake it has. Buttoned everything back up, battery, washer tank, etc. Now, the thing does not want to idle and is missing under normal load. It did throw a CEL for a misfire on all 4 cylinders.
Out of ideas, I put the original plugs for cylinders 2 & 4 back in and that had no effect. I am baffled. I know that the filter oil can accumulate on the MAF sensor and cause a running issue. Could that be causing this misfiring issue?