The fuel distributor COULD be the problem. When meting out small quantities of fuel at idle, irregularities would tend to show up more than at a high rate of delivery. At idle, the metering slits keep the secondary pressure low enough that rates could vary significantly from injector to injector.

However, there are a lot of other possible causes of your symptoms. We can't know for sure what your tech has done to eliminate other possibilities, but some tests are pretty simple. For instance, to rule out a worn pot in the airflow meter, disconnect the EHA. If idle smoothes out, then the fuel distributor is NOT the issue. Likely the airflow meter pot has a worn spot.

Steve

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