I have a fairly involved question about my car. My car seems to be equipped with a mass airflow sensor, as well as two oxygen sensors (one upstream of the catalytic converter, one downstream). Recently I have discovered a sizable crack in the boot connecting the MAS to the throttle assembly, and I’ve already ordered a replacement. However, this is making me wonder how my car operates.
- The check engine light is NOT on
- My gas mileage seems a bit lower than it used to be
- My engine temperature seems normal
I guess my question boils down to:
a) What is the chance that the engine is actually running significantly leaner than it should be without illuminating the check engine light? Is it possible the ECU only uses the input from MAS for mixture control and uses the oxygen sensors only for cat sanity checking?
b) Would running leaner actually decrease gas mileage noticeably?