If the idle is surging up and down, you might check the rack damper bolt. It's on the rear of the injection pump on the bottom. You'll see it if you look between the oil filter housing and the IP. If it's silver colored you may need a new one. There is a new updated style one that is gold colored. You can adjust the rack damper bolt if you loosen the lock nut on it then back the bolt out of screw it in. Lots of info on here about the rack damper bolt (a.k.a. governor idle adjument pin).

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