What would make the Engine Shake and Gas Pedal stick in a 1986 Mercedes-Benz?

[ElissOnaldso]

Found a 1985 Mercedes-Benz I was looking at buying it only has 96,000 miles and is going for $599.00. The lady said it drives good, But the Engine shakes and the gas pedal get stuck some times. What would cause this and how much do you think it could cost to fix in the long run. Is it even worth my time?