I,m researching mass air sensor info. Just sort of inherited a nice 1994 Explorer XLT thats been pretty well looked after, but was running horrible rich & a lousy idle. Check Eng. light proved to be MAS. Changed it with one from wreckers. Idle now perfect & motor running cleaner. Oddly though Eng.check light is off when motor started and stays off untill revs increase to about 1600rpm when it then comes on & stays lit untill motor's stopped. Anyone had same problem or have a comment? Oh! should add, the check eng.lght coming on seems to have no effect on engine power when travelling and idle is still A1.