My 87 iroc has been running rich, it was throwing codes for the maf burnoff relay and I replaced all maf relays, now it is throwing the manifold air temp sensor, the car runs ok, has an occasional hesitation but u can smell the gas coming through the exhaust, any ideas?

 

Several things can cause a rich running engine. An open MAT sensor could cause it. Other common causes are a ruptured fuel pressure regulator diaphram. With the engine running, disconnect the vacuum line that goes to the regulator and look for fuel coming from the regulator vacuum port, through the line. Leaky injectors, including the cold start injector, will cause the engine to run rich also. The cold start injector is operated by a cold start switch that is located at the front of the motor. The switch is closed when the engine is cold, then opens after the engine is started. You can check for the injector to be operating after the engine has started by simply unplugging its connector and listening for the idle to change. Wait for 20 seconds after the engine has started as some have a decay timer.

A MAF that is reading incorrectly can cause either a rich or lean condition. An O2 sensor that is shorted will cause a rich condition. It is fairly common for the engine coolant temp sensor to read incorrectly and cause the system to run rich. The best way to check all of these things is to use a scan tool with data stream to view the data for each of these sensors and also short and long fuel trims(integrator and block learn as they are known on the ODBI systems).

 

Thanks for the response, I will begin checking the things you mentioned. Hopefully get this figured out.