1987 420 SEL - Faulty Cruise Control Amplifier

[wscheffer]

My 1987 420 SEL’s Cruse Control surges about a 1/2 mph back and forth about every three seconds or so when engaged and is just enough to notice a fluctuation in speed. It does not matter what speed it is set at. It is a constant from the time it is turned on until it is shut off. You can see the economy gauge moving back and forth in sync, like it should under this condition. The engine runs perfectly when the cruse is turned off. My thoughts are that the Cruise Control Amplifier maybe at fault causing the drift in speed

 

[television]

My 1987 420 SEL’s Cruse Control surges about a 1/2 mph back and forth about every three seconds or so when engaged and is just enough to notice a fluctuation in speed. It does not matter what speed it is set at. It is a constant from the time it is turned on until it is shut off. You can see the economy gauge moving back and forth in sync, like it should under this condition. The engine runs perfectly when the cruse is turned off. My thoughts are that the Cruise Control Amplifier maybe at fault causing the drift in speed

I cant find any digrams but I feel sure that this is part vacuam controlled.

Any leaking poor fitting pipe could do this. Not 100% though on this issue.

Malcolm

 

[stever]

I think that the systems on later cars are all electronic - the earlier (e.g. pre 1980 or so) cars have an electronic amplifier with vacuum actuator. My understanding is that the amplifier is the usual culprit in faults such as these. Probably best to refer to an auto-electrician.