Remove ALL tension from the throttle cable. It should wiggle just a little bit with your foot off of the pedal.

If that does not fix it, the vacuum system must be re-mapped with extra focus on that line that leads to the back of the injection pump.

First test should be removing that line that goes to the back of the IP. Next time you have high idle, pull that tube off and make sure the throttle cable is slack, completely.

If that does not fix it, you need to spin that metal vacuum sensor on the back of the pump, that is the idle adjustment.

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