So here is a little back ground.
I bought an 03 wrx from my old boss. We used to work on cars together the man is a very talented mechanic. He helped his friend do a full rebuild on the car after the thing overheated and warped the heads. They bought a new short block from EFI on 7/5/11. the bought re-manufactured heads from a shop in CT. the car was assembled and then driven for around 5000 miles. on 11/29/11 the car was taken to a shop in brooklyn where the vacuum system was smoked and found no leaks. they also checked live data and found nothing. they suggested it be brought to a Subaru dealership in their notes. on 1/3/12 the car was brought to EFI and checked. the receipt has labor for diagnose misfire, replace coil packs and A/C tensioner. There are no notes as too a solution or what the problem was. this is the last receipt I have before I bought the car in july of 2012. I was told the car had 5000 miles on the new engine and there was 115000 on the body. The car had a CEL that would come and go for a misfire on all 4 cyl. Car drove fine but idled a bit rough.
Fast forward to today. I have put about 40k on the car. I commute 100 miles each day all highway. Lately the CEL has stayed on and it will flash if I accelerate rapidly. I fell also as if the idle has gotten worse. I followed the thread that donkey posted as well as some other online forum research I have tried.
I have to date replaced the spark plugs (NGK Iridium properly gaped), I cleaned the MAF (also unplugged and misfire stayed), I know that all 4 coils have been replaced, I have cleaned the battery terminals and coil pack grounds, I added grounds to the car, I know the car was smoked for vacuum leaks but I also checked with spray for a pickup in RPM's and got nothing, and lastly today I ran a compression check and got between 165-150 on all four on a cold engine.
The car is stock. and the codes I am getting are p0301-p0304. I at one point had a multiple cyl misfire but I am no longer getting one. My last theory in which I know nothing about is that the is something programmed into the ecu. The car came with the original Cobb access port. I am thinking that maybe there is a map in there that might not agree with the car. Any thoughts or input is greatly appreciated. I am a very competent mechanic and have access to just about every tool I could need except Subaru specialty tools. I can't really afford to bring my car in and have them run up hours of diag on it so I'd like to use that as a last resort.