Slight miss at idle
 

I have a slight miss at idle.
It is mostly felt in N or P, not so much in D.
It idles fine but every 30 seconds or so a jolt is felt and the revs seem to drop slightly.
Spark plugs are 2 years old, 2,000 miles or so.
Leads never changed.
O2 sensor never changed
Fuel filter never changed to my knowledge.
62,000 miles, E220C (M111.960)

Thanks

My guess would be, that if it only has 2000 miles on it in 2 years, it may be carboned up, which a longer trip might fix, or the gasoline migh be getting stale, again a long trip might help.
Gilly

When I take it out it does go on long trips. I only put about 15 liters of gas in it at a time so it's never older than about a month or 2.

I cannot tell you the exact mileage per year, but each time it comes out I put at the least 30-40 miles, at times up to 100+ miles, and it never goes more than 3 weeks between drives.

I do assume it's carboned up though. Is there a way I can clean it? I saw some videos on youtube where something is sprayed into the combustion chamber via the spark plug hole, then it foams up, and it is taken out via high pressure air.

Spetz, instead of using cleaning agents you might try driving your E220 in a lower gear (with higher engine RPM) to help remove the carbon deposits. Somtimes referred to as an "Italian tune-up".

Would that clean everything up though? Don't forget that car has 62,000 miles and it was my dads car who didn't drive it fast hence there should be considerable build up, no?
I was looking at this video:
http://www.youtube.com/watch?v=kgqYdmH2UOg

And it comes out very clean. It's done to the same motor as mine.

A hard run might blow it out; like was mentioned, an "Italian Tuneup". Wouldn't cost anything to try it. What octane are you using?
Gilly

OH, and also, if you are concerned with "getting it all out" , then there is no real hope, you are fixated on the cause, not the problem. In my mind, you should want to fix the problem, the slight miss at idle. If you want ALL the carbon out, forget it, you never get ALL the carbon out, unless you want to take the heads off, have it all cleaned out, and never start it again. In that case ALL the carbon is gone forever. You run the engine, you get carbon. If the engine is never driven hard, it accumulates and can cause problems. Other things worsen it as well. But more than likely, it's just accumulating because it never is driven very hard. You can just take a sparkplug out and see how much is on the top of the piston, but if you don't know what a normal amount of carbon looks like, it might not be all that useful to even look.

Right now I generally like to floor it through 1st and 2nd gear a few times each time I drive it with the idea that at the least it shouldn't build up any more carbon than it has.
Even if it doesn't fix the miss, cleaning up the carbon will still make the engine run better won't it?
Plus, seeing as I don't know where the miss is coming from, is cleaning the carbon a good way to go? I was thinking of that + running some injector cleaner through it

Most injector cleaners will say they do remove carbon, although I'd be a bit skeptical.

"Techron" is a good injector cleaner, it could very well be part of the problem.

Gilly

There is no techron available here. Also I read that with techron it mixes with the oil and needs an oil change after using it? I just did an oil change and the next one isn't scheduled until March 2011.
I was reading very good things on the BG 44K injector cleaner if you have heard of it?

No I haven't. I've also never heard of such a thing as needing to change oil after using techron though

Someone told me that if you add Techron you need to change oil after it. In fact I think it says so in the directions on the can.

To be honest my goal is to make this car like new, however I have never had such a high mileage car before so I am unsure of what I need to be doing. I've asked a few times on these boards (and others) what I would need to do at 62,000 miles but got no replies. I know some cars need timing belts changed at this mileage but from what I research the M111 uses a chain and doesn't need replacement

Spetz, your engine should easily last 200,000 miles if maintained properly. Use the grade gasoline and oil specified in your Owner's Manual; change the oil, oil filter, air filter & spark plugs per MB recommendations ... simple enough to do.

Yes but at some stage it needs a major service doesn't it?
I have never done a diff fluid change on it, neither spark plug leads, also quite possibly never a fuel filter.
When should these be changed?
And what else should be changed?
I have recently changed plugs, air/oil filters along with oil change each time, tranny flush, coolant flush, engine/transmission mounts, AC regass, and pressure switches for fan.
I don't think even the throttle body has ever been cleaned though. Intake runners/plenum must also be pretty dirty. Do catalytic converters or mufflers need replacing?

The car runs really well but just doesn't seem to be "like new". I have a feeling there is one or a few minor things with it which need replacing but I cannot tell which

It sounds like you are looking for things to do, even though nothing may actually be wrong. Keep in mind your car isn't new anymore even with the low mileage so to you it may never feel "new". A full service with your mileage would consist of changing all the fluids, filters, cap & rotors, wires. All of the required service & maintenance with intervals should be in your owner's booklet.