Seems likely it's the airflow meter pot, if disconnecting improves idle. It is part of loop control in that it tells the ECU when airflow demand is changing and in need of enrichment. If this is a false indication due to malfunction (poor contact of wiper), then enrichment will cause the ECU to lean the mixture back out - increasing airflow by opening the ICV and speeding up the idle.

Steve

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