Last summer my 5.0L 1999 Explorer engine check light illuminated. Outside temperature was 90 degrees altitude 1100 feet. Car would periodically run rough when idling occassionally to the point of chugging. Shop check of codes (three times) showed nothing in storage. Battery disconnect/reset - light would return but not instantly. 95 % of the time engine ran ran smoothy even though the caution light was on. Rough running seemed to occur most frequently after fuel but that may be coincidental. In the fall as the weather cooled the check light went out (engine ran smoothly) only to illuminate again last week. This time the AAA care care center found a P1409 code which they described as a mass air flow problem indication. Surfing the web I found reference to the Electronic Vacuum Regulator under P1409. Should I just change out the EVR unit. Tks. Don
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P1409 - 
