Don says... even with the new fuel delivery systems they can carbon up. The first step is to do a "power purge" or "carbon blast". They start the car through the intake with a half can of this stuff and then let it sit for 20 minutes. Then they either do it again or add the other half of the can to the gas tank (I got a different take from the mechanic who actually does it) and just let it idle until it stops blowing smoke. If it doesn't stop blowing smoke, the $35 spent is worth it to find out if there may be a more serious problem.