Rotating the pot body while the engine is running IS how you make the adjustment. If the engine runs ok when you start it, leave the pot in that position until up to operating temperature, and idle has stabilized. If voltage reading is out-of-range, then make a very small rotation, and wait until idle has restabilized before remeasuring. Repeat until correct.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7