my car keeps accelerating on its own, why?

[Jeru]

For the past 3 months my car accelerates on its own. I fix the timing by turning a screw behind the engine, but after driving for about 2 hours the car will accelerate on its own again. I know I can't ask for much because it's an '87 Chevrolet Spectrum, but at else I can try diminishing the problem in some way.

[silentwarrior]

I am not sure if this car is throttle body or carb. If it's throttle body, it could be a sensor.