Unless I missed it, I don't see that you have replaced any of the idle air circuit or intake rubber. If this tubing is not soft and pliable, it could have cracks, and at least will not seal properly at joins. I would replace all this rubber - it is pretty cheap if purchased here. Don't forget the lower part of the air intake plenum too. Also clean the airflow meter vane to insure smooth operation when slightly open. A problem in either area would be much more noticeable cruising and under very gentle acceleration than full power acceleration. Typically idle might be a bit high and erratic, too.

Steve

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