How is your W124 OVP unit?

Some 80,000 miles ago (around 360k) My 603 (although W126) had a periodic surge and periodic high idle while driving in stop and go, and occasionally at start up. Enough surge to move the car forward with light acceleration even though the foot was off the fuel pedal. I'd hover my foot over the brake at times to be ready to check the surge. Kind of unnerving.

Replaced the OVP for under $20. First "new" aftermarket unit was a dud. Second one has cleared the surge /elevated idle for the last 80k miles.

I'd also do the workup Mxfrank is suggesting & check Diseasel300's diagnostic points.

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1986 300SDL 440,xxx