I took my mom's 1984 380SL to the smog station, and while the car passed the HC and CO tests on the dyno with flying colors, the car had a high idle, it was in 850-900 range, when spec is 650RPM. Just a few moments ago, i took my Craftsman DMM, set to duty cycle, i had a wildly fluctating duty cycle of 60-70%. What could be wrong? i tried to fix it previously with a new fuel timing valve and a new O2 sensor.

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1984 380SL-driving and service privileges.