Download ISSUE SERVICE TIP. This TSB article is a diagnostic procedure to address vehicles that exhibit lean driveability MASS AIR FLOW (MAF) DISCUSSION symptoms and may or may not have any Diagnostic MAF sensors can get contaminated from a variety Trouble Codes (DTCs) stored in memory. of sources: dirt, oil, silicon, spider webs, potting ACTION compound from the sensor itself, etc. When a MAF sensor gets contaminated, it skews the transfer Follow the diagnostic procedures described in the function such that the sensor over-estimates air flow following Service Tip. The revised diagnostic at idle (causes the fuel system to go rich) and procedure is a more accurate means of diagnosing under-estimates air flow at high air flows (causes the symptoms. fuel system to go lean). This means Long Term Fuel Trims will learn lean (negative) corrections at idle and learn rich (positive) corrections at higher air flows.