Greetings Dude,

Here is the removal process and the I.D. of the cruise amp or as someone called it the ECU (electronic control unit) none the less it's a cruise amp. www.gdl-online.com/remove.html

Based upon what you describe I think it is still the amp that is at fault. You can check your vacuum fittings and hoses all you like but your year car should contain an all electrically controlled cruise control system. The early models had vacuum going to the actuator under the hood, my '80 does, but my '84 doesn't. Try the resolder job unless it's more than you want to undertake, then I'd send it to GDL for testing.

Charles

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'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan