Car dealer report the computer code problem as P2178 and/or P2188.

P2178 Fuel System Too Rich At Off Idle Possible causes •Base engine problem (e.g., low engine compression) •Fuel injector problem (e.g., one or more dirty or restricted fuel injectors) •Fuel line pressure too high (check fuel pump and fuel pressure regulator) •HO2S connector is damaged (check pins for damage, and for moisture) •HO2S has failed (it may be contaminated with fuel, silicone or water) •HO2S heater has failed •Purge solenoid valve operation problem (the valve may be stuck open) •MAF sensor has failed (it may be dirty or out of calibration) •PCM has failed •Positive Crankcase Ventilation (PCV) system or valve problem •Relief valve (built into the fuel delivery pipe) has failed •Spill valve control solenoid (built into the high pressure fuel pump) has failed •VCTS problem or improper operation •VVT problem or improper operation Customer Concern: Has a code P2188 indicating the fuel system is rich. Tests/Procedures: 1. Double check the Mass Air Flow (MAF) sensor reading at normal idle. A good reading would be about 3 g/s. If the MAF sensor is reading 4.9 at idle try cleaning it. Mazda also has TSB 01-006/06 that addresses a potential MAF sensor ground problem and a terminal repair kit. 2. Block off the purge hose and recheck the fuel trim. If the fuel trim is now reading normal the purge solenoid may be stuck open. Mazda also has TSB 01-052/06 for a possible purge solenoid sticking open, however, those usually cause a lean condition. All you need to do is clean the Mass Airflow Sensor

This may be related to the purge valve solenoid being stuck in the open position. It is part of the fuel line system.