NorseWagon

A few weeks ago, at 95K miles I changed all 16 plugs and the plug cables.
Used Bosch Platinum plugs and Bosch cables, good German products..

No vibration noticed, smooth.

A few days later I took the car to the MB dealer for a 4-wheel alligment, brake fluid flush and change of valve cover gaskets.

Got it back and noticed a slight vibration when in idle, other than that, normal operation, normal power and fuel consumption.

Took it back to the dealer and had them plug it in and suggested they could have knocked a plug wire loose when doing the other work.

They found misfiring in the # 7 cylinder and checked the plug wires, no loose ones.
The tech mentioned it could be a dirty injector or a valve problem.

Ran a tank with injector cleaner, do difference.

Any ideas...?

jimbo1763

Ever had the motor mounts checked/changed?

NorseWagon

Yeah, changed the motor mounts almost 3 years ago, no problemes there:
Had the dealer go over the wagon with a fine tooth comb 2 weeks ago as the warranty expires next month and I want every little thing fixed.

The vibration is "uneven", not a rough idle, but the occasional little jolt every few seconds when in park or neutral and idle. Harder to detect when in gear and on the road it runs smooth....

MercFiveHundred

I've always had that little jolt and my dealership says it's normal. I bought it preowned at 57,000 miles. I'm at 191,000 and still doing the occasional jolt at idle/park. What i noticed is when im in park and i rev up to like 3k-4k rpms (up and down), then let go, it will jolt more in frequency. My guess is it's something to do with the comp? I dunno, like you, it's smooth accel and crusing.

NorseWagon

Hmm, no don't think it is normal as I never noticed it before AND the dealer detected a mis-firing on the # 7 cylinder.

The question is rather what is causing the mis-firing? Not the plugs or cables as I just replaced 'em. The injector? The coil? The valves?
Guess I will have to get my hands dirty moving plugs and coil around to see if the problem moves too.....

NorseWagon

Yup, the issue bothers me..hence this thread.

How do I run the test..? Guess I will go DAS Xentry and find out...?

Don't be shy, feel free to drop more details instead of being mysterious.

NorseWagon

Right, no mystery and I don't have a clue what you are talking about...

MPOW33R

I have 151k on mine. Its had that same little "jolt" Im on my 3rd set of plugs and 2nd set of wires. Still the same. Fuel consumption and power band as equal as day one.

Does bug me a little when I think about it. But in general my thoughts are
"it can be worse"

Would be thrilled to hear of your findings. I have exhausted my mechanics and many forums and MB owners. Id say 90% of them experience the same issue. Leaving 10% to say nope my idle is very smooth.

ozusa

Just to check, you firmly mean the jolt is with the engine and not the transmission and can be seen/felt in park? That is, you don't have the low-speed jerkiness in the transmission that can happen.

Anyway, just one quick point: New parts does not necessarily equal perfect parts. Try swapping another plug and/or plug wire into 7 and see if the issue goes away or moves.

NorseWagon

I was in the 10%, not sure what happened..

,

Yup, that is what I mean, the "jolt" is there in neutral and park as well as in drive.

Have not had time to deal with it, heavy work schedule this summer, but will report back when I start moving cables and coils around, althought without a plug in diagnostic tool I may move the problem to the # 6 cylinder, get the same result and not knowing which cylinder it came from.

NorseWagon

Looks like the jolt is gone...:

Pulled both plugs and cables of the Nr. 7 cylinder and re-installed.
Found tiny amounts of green corrosion on one of the cables.

Now it idles like before..