I don't know your car, but the symptom is of problems occuring durig a return-to-idle condition. There are various switches and sensors involved I would check that detect this. You should have a throttle position sensor on the throttle shaft at least, and probably an airflow meter potentiometer as well. If the latter is original, it is likely worn out.

Steve

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