I've been using an old '95 Lancer GLXi (itlog) from my dad's office for the past few days, and I've been bothered by the fact that the check engine light keeps turning on.

Upon closer observation, it happens whenever I go past ~70 kph, no matter how low I keep my revs (i.e. 5th at 1.8k rpm).

The light only vanishes when I turn the engine off. Even after starting the engine again, the light doesn't turn on, at least until I hit 70 kph again.

I've had my engine fluids checked (oil, brake, power steering, etc) and all where within normal levels. Temps were fine too.

I plan to have the car checked soon, but I'd like to hear the thoughts of seasoned troubleshooters on this case, just so I know what to expect when I send it over for repairs. Thanks!