P0102, P0121, P0108 Fault Codes in 1997 Monte Carlo 3100 V6 - Diagnosis and Fixes
My 1997 Monte Carlo 3100 V6 has started running poorly after I replaced the upper intake gasket to check for a fuel leak. Since then, the vehicle has triggered multiple OBD-II fault codes: P0108 (Manifold Absolute Pressure Sensor), P0102 (Mass Air Flow Sensor), and P0121 (Throttle Position Sensor). All three codes appeared simultaneously, which is unusual since the car was running fine prior to this. I've already checked fuses, cleaned the MAF sensor, and inspected wiring and connections for damage or loose contacts. However, I'm still unsure of the root cause. Could these codes be related to a vacuum leak or unmetered air entering the engine after gasket replacement? Any insights or troubleshooting steps would be greatly appreciated. Thanks, CJ
If these fault codes appeared only after replacing the upper intake gasket, it suggests a potential vacuum leak or air ingestion issue. Recheck all your work—ensure the gasket was properly installed and that there are no gaps or missing seals. Inspect wiring harnesses for cracks, frays, or loose connections, especially near the intake manifold. Also verify that no unmetered air is entering the engine, as this can trigger multiple sensor faults like P0102 and P0或P0108. Cleaning the MAF sensor may help, but if the issue persists, a vacuum leak test is essential. Keep us updated on your findings.