1999 Silverado Running Rough with P0446 and P0102 OBD2 Codes - Troubleshooting Guide
My 1999 Chevrolet Silverado is experiencing rough idling and poor performance, accompanied by OBD2 diagnostic codes P0446 (Evaporative Emission System Vent Control Circuit Malfunction) and P0102 (Mass Airflow Sensor Range/Performance Problem). I'm looking for reliable troubleshooting steps to resolve these issues. Any advice or common fixes would be greatly appreciated.
Start with basic diagnostics: - Clean the Mass Airflow (MAF) sensor and inspect for vacuum leaks downstream of the MAF. - Try the 'spray test' using carburetor cleaner to check for vacuum leaks. - Do NOT use an oiled air filter, as it can interfere with airflow readings. For P0446: Check if the vehicle has any issues during refueling—does it hesitate or stall when filling up? Try pumping gas slowly and observe behavior. - Verify that there is 12 volts at the vent valve's pink wire when the engine is off (KOEO) — this is critical for proper evaporative system operation.