Hello Everyone,
I just changed the battery in my 1999 ML 430 with 70k, last night it left me stranded it was the original battery so probably my fault for not changing it. I replaced it with a battery from MB, I figured the original replacement would be the way to go. The only problem now is that it is running rough. At idle it's fine, once you get above 2-3k rpm it breaks up and runs poorly. Any ideas what this might be? It ran fine before it died. Maybe I need to reset something? Any help would be greatly appreciated.

Note: Before the battery died the CEL was on for about a month or two, when I pulled the codes they were all misfire codes, one for each cylndr., or a few cylndrs. can't remember.

Thanks Again!

Your mileage coincides with an impending MAS failure as well. A bad one will send all sorts of erroneous fuel-air info and basically, performance will suck!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Thanks for the reply. Yeah I was kind of thinking the MAS would be it, just weird that it ran fine before the battery died, now with the new one it's running crappy. I was also thinking the crank pos. sensor could be bad, but it sounds like the symptoms of that is the truck stalling, which is doesn't. I'll get an OBD II on it and pull some codes. What are codes for a bad MAS? Thanks again!

This condition could also be related to bad coils. I believe that there is 1 per cylinder. These are known to fail. My 2000 had a coil failure that ran like you described.

Any specific way to test the coils to see if they are bad/faulty?

Ric,
Ann Arbor
2000 ML320, 118k

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Ric
Ann Arbor
2000 ML320, 172k

If you think education is expensive, try ignorance.

I'm sure that there a test, but I'm not that knowlegable. Maybe someone else could help...

Well it runs better then it did, however at full throttle it still breaks up. All of the codes are misfire codes so maybe one of coils are bad. I kind of thought that because with the hood up and it running I heard a tapping\snapping noise coming from the top of the motor, almost like it was arching out. Now what coil it is might be tricky to figure out.

it may just be a bad plug wire. You might try pulling one wire at a time, then start the engine, and see if the noise is gone. That may work to isolate which one is bad.