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Q: runs rough on 1998 Mercedes-Benz ML320

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Our 1998 ML320 when you start it up sometimes will lose power when you push the on the gas pedal almost as if its not firing on all cylindres and the check ingine lite is on. so we took it in and was told 3 cylinders were misfiring so they replaced all 12 plugs and wires and it ran great for one day and the same problem is back? also if this happens all we have to do is shut the car off and start it back up and the problem goes away until we restart it. Is there somrthing elec. that could be going bad?
plugged cat, if cylinders 1-2-3 are miss firing, the passenger cat has failed. if cylinders 4--5-6 are the problem, drivers side cat has failed.....big bucks......
I have a 2000 ML320. Had the same problem. I happens when the RPM's exceed 5500 RPM. (If you have a tachometer you can follow the rpm cycle as you drive). Mine has a automatic transmission. If you accelerate with a bit of a heavy foot, at the tail end of second gear, the RPM gets up 5500 and beyond. If you want to avoid the "3 missing cylinders" and the engine light, keep an eye on your Tac and do not exceed 5500 RPM which you are most likely to do in second gear. Hope this helps,
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