My 2002 WRX has been suffering from off and on sputtering fits over the last few weeks. The only mods on it are a turbo timer, 3 inch exhaust with out Cats, STI intercooler, and hallman boost controller. I have replaced the MAF, O2 sensor and Exhaust Temp sensor and it still will randomly sputter out and die. when it goes through these sputtering spells it backfires when the accelerator is pushed, I can see some gas coming out of the tailpipe and there is gas in the oil. For some reason it is running really rich. I took it to my mechanic and he could not find any error codes and it doesn't seem to act up when he has it, however when I get it it happens within the next couple of days. Its driving me crazy, can some one help me??