'95 Eldorado engine surge

This is an enquiry for my father-in-law who has owned the car since new.

Symptoms:

While driving, the auto will begin to accelerate without the gas pedal being depressed. With

foot removed from the gas pedal the auto will continue to accelerate and go faster and

faster until the brakes are applied. After the acceleration/breaking cycle has occurred once

or twice the automobile will then function normally for the remainder of the trip.

A local mechanic has attempted to solve the problem by clamping off an air-line which has

solved the problem somewhat but now the engine idles at a (slightly) higher RPM than

normal/previously.

Any ideas?

Thanks in advance.