check the fuel pump. unbolt it from the block but leave all the hoses connected. Squeeze the primer ball. If any fuel comes out from the back you have a bad diaphragm. The leaking fuel goes directly into the crankcase causing erratic idle. It would also run kind of rich. If thats not it I believe that motor has an idle stabilizer module on it. It manipulates the timing to achieve proper idle. Use a timing light to see if the timing is all over the place. If you disconnect it and it idles steady then it is probably bad.
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