I'd also check the 'throttle control element' which is the little cupcake
size bellows unit that's located on top of the engine.  It pulls on the
throttle when you have cruise control set.  My 88 Vanagon cruise control
behaved like you are describing and I found a tear in the rubber bellows.
Since my leak was small, I temporarily just put a layer of silicone sealer
over the area, let it cure overnight and it worked 'better' until I could
get a new unit.  It's easy to check.

Hope this helps.

John Graham
88 Westy - Charlotte, NC

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