I recently bought a 2007 Toyota Corolla LE and the check engine light went on a week after my purchase. I took it in right away and was told it was a faulty Mass Air Flow censor. I got it replaced and the light came on again 10 hours later. I took it back, they said it was the Mass Air Flow Censor, again, and they kept it for a couple days. Said I was good to go. The light came on again an hour later. I took it to Autozone to have it scanned and it said SYSTEM TOO LEAN. I called the dealer and they said maybe the air filter cover was not on securely, I lifted it and put it in the slots and back on completely and he said maybe it would go off after a number of "cycles" it is still on. What should I do?