Having a misfire problem on cylinders 2 and 4. The idle is really rough and I'm getting a CEL on cylinder 4 (P0304) and also the CEL for the random misfire. I've tried the usual already, including swapping coil packs, injectors, installing new plugs, cleaning the MAF sensor, and installing a new fuel filter.
I took the car to a local mechanic and he ran cranking compression, running compression, and leakdown tests getting the following numbers:
~130 psi for all four cylinders during the cranking compression test
~ 65 psi on cylinders 1-3, and 40 psi on cylinder 4 during the running compression test
~20% leakage on cylinder 4
This suggested that there may be a valve problem, so I took the car to a subaru dealer in bakersfield, ca, roughly 110 miles away, and yeah, that's the closest dealer.
The dealer performed a compression test again getting the same numbers and did a leakdown test on cylinder 4 getting only 2%. I don't know how there could be such a large discrepancy between each leakdown test performed.
The techs at the dealer then thought it could be the ECU sending incorrect signals so they replaced the ECU, which changed nothing.
Then they thought it was bad gas, so they are ran out the gas in the car and put in the gas they use at the dealership, again no change.
I'm at a loss right now, they want to charge me ~$800 to open up the head to see if it really is a valve issue, but there's no guarantee that's the problem.
Does anyone have any ideas on what to try next, I'm so stuck!