Hi everyone, my 2004 Mercedes-Benz SL500 (R230, M113 V8) has been experiencing some RPM shaking issues.
When starting cold, once the RPM drops down to normal idle, the engine shows a slight idle fluctuation. It’s not a big shake — the tachometer needle just moves up and down within a very small range, like a subtle idle instability.
While cruising on the highway at around 65–70 mph, with RPM below about 2000, I notice a very light vibration and the RPM needle also fluctuates slightly. But if I increase the speed to around 85 mph, with RPM at about 2500, the vibration completely disappears and the car becomes very stable.
I’ve also noticed a pattern: if I drive from Erie, Pennsylvania to New York City, the car becomes very smooth right after I exit the highway — almost no vibration at all. But after driving in NYC traffic for a while (stop-and-go), the mild idle fluctuation and slight vibration come back.
I drive very gently, like a chauffeur, and I change the oil frequently. The engine has no oil leaks. I’ve also tried adding a fuel system cleaner, but the issue didn’t fully go away — the symptoms are still there.
Could this be caused by spark plugs or ignition coils? Or maybe the MAF sensor?
Any advice would be greatly appreciated.
Thank you!
When starting cold, once the RPM drops down to normal idle, the engine shows a slight idle fluctuation. It’s not a big shake — the tachometer needle just moves up and down within a very small range, like a subtle idle instability.
While cruising on the highway at around 65–70 mph, with RPM below about 2000, I notice a very light vibration and the RPM needle also fluctuates slightly. But if I increase the speed to around 85 mph, with RPM at about 2500, the vibration completely disappears and the car becomes very stable.
I’ve also noticed a pattern: if I drive from Erie, Pennsylvania to New York City, the car becomes very smooth right after I exit the highway — almost no vibration at all. But after driving in NYC traffic for a while (stop-and-go), the mild idle fluctuation and slight vibration come back.
I drive very gently, like a chauffeur, and I change the oil frequently. The engine has no oil leaks. I’ve also tried adding a fuel system cleaner, but the issue didn’t fully go away — the symptoms are still there.
Could this be caused by spark plugs or ignition coils? Or maybe the MAF sensor?
Any advice would be greatly appreciated.
Thank you!
The possibilities are usually, motor transmission mounts, spark plugs and wires,. This also could be coil packs , vacuum leaks, and possibly driveshaft flex discs/ carrier bearing, in my experience failing MAF doesn’t cause random misfires, just erratic idle behavior/ stalling.
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