My daughter has a 1999 C230- about 105k miles. Gets P0302 code and rough engine. She can clear code (requires restarting engine). Engine is now smooth and CEL stays off (no code) until she accelerates hard ("changes lanes") again, sometimes longer. She's changed plugs, flushed injectors. Dealer wants to flush tank. Could it be MAF? Anything else to test, check or replace?