I just bought a 2001 Ford Mustang cobra. It has exhaust, throttle body, air intake, and a few other things. I drove it home from the place and the check engine light came on and the idle was jumping from 800-3000 rpms on its own. It did it most of the way home. I hooked up my codereader and it said that the system was lean. Thats he mass air flow sensor. I brought it back and the guy said it was because the car has a lot of modifications but no tune. Is there something wrong with the car or would that be the problem?