Grand Marquis - check engine display light
1994 Grand Marquis, 99,900 miles - good reliable vehicle. "Check engine" dash display light has just begun to come on as vehicle exceeds 60-65 mph. Must shut off engine to clear "check engine light." All fluids have been checked and are OK. Air intake is clear. I installed new air filter. Short of a visit to service tech, what else should I check? Air sensor? Any suggestions welcome.