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Old 12-12-2001, 09:47 AM
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Question Idle - slight RPM fluctuation 420 SEL

My '91 420SEL (151K miles) has an ever so slight, regular variation in the RPM's at idle - it is barely noticeable, I can hear it and see it in the oil pressure gauge (once engine is hot), but it is almost unnoticeable at the tach. BUT I CAN HEAR IT! The idle speed seems to fluctuate EVER so slightly, almost rhythmically, every 1.5 seconds? The overall speed on the tach seems to be right on: 500 RPMs in gear, and aprox 700 in neutral.

Background - I recently had a miss/stumble that was cured by various ignition tune-ups: replaced plug wires, distributor cap, rotor, spark plugs, as well as O2 Sensor. I also had the Motorvac service on the injectors.

Is this slight fluctuation just me being over sensitive???? Is this normal, and I just didn't notice it with the other problems on my car?

Any suggestions/insight/advice would be appreciated

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Old 12-12-2001, 10:05 AM
Ali Al-Chalabi's Avatar
Senior Member
Join Date: Nov 2000
Location: Knoxville, TN
Posts: 1,837
Very small fluctuations in idle speed are normal, the car can't be that exact.
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record
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