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Reving up and down at idle

Started by jackbof, 25 May 2024, 04:30 PM


Hi all,

I have a 1975 350SE and it will idle nice and smooth when I start it but as soon as I touch the fan AC fan speed control ever so slightly it will start to rev up and down continuously. If I turn the fan off and fiddle around with the controls a bit it will return to a smooth idle. Sometimes while driving it will just do it randomly at idle but its smooth when throttle is open.
Any ideas on what might be causing this?


For a start have a look at the a/con vacuum advance  compensator which is on the firewall engine side . It is an electric solenoid connected to the distributor.