I just bought a C36 and it got a check engine light for MAF also the idle is running rough. I bought a new MAF from Dealer but when i installed, it was sag/cut out to rev higher rpm. So, i put the old MAF back and it run better. . Sometime the car idle fluctuating between 500-1500 rmp? Do u guys know what wrong with it? What's the most common problem on this car?

Thank you