Newbie here, we have owned many Mercedes and this S550 is nicest car yet --40K miles on it. We paid $1000 for diagnostic and ignition coil repair. Get car back and 2 days later starts doing the exact same thing--engine light on and stuttering, hard idle. Then the next time I drive it -- totally fine. Then the next --back doing the same thing so it is intermittent. Is it possible to do these myself --has anyone repaired them? Thanks.....

 

moved to W222 forum...

 

Changing out a coil is pretty easy and straight forward. All you have to do is remove the engine cover, air intake, air box (disconnect electrical connector) and a foam pad that sits on top of the coils. The coil has two E torx bolts holding them in and an electrical plug. Hardest part is just pulling it off the spark plug. I assume you have a Scanner to identify which coil is bad but it not just get a basic one as that should be able to identify which cylinder is having the misfire. If you have basic mechanical skill you should be fine.

 

This intermittent problem could also be caused by bad/contaminated gasoline.

 

Its pretty simple to replace, but getting the plugs off can be difficult. You will probably break one or more of the rubber boots. They come with the coils, but you can buy them separately for around $20 each.
You can get a whole kit with 8 plugs and coils at FCP Euro for around $500. 40k miles isnt a lot, and the coils should last longer, but like anything else, its not a bad idea to just replace them every decade or so. Just depends on your risk tolerance.
They have kits for a lot of maintenance items

A spark plug wrench is also available. its just a long thin 17mm wrench. Makes things a bit easier and less chance of breaking things. They are about $20, just search for Mercedes Spark Plug Wrench.
The E torx are E10 if I remember correctly. You can get a small E Torx set for around $13. Definitely get that too if you want to do anything on the car. Don't use regular sockets.
Getting the connectors off the coils can also be a pain.

 

I had the same problem over and over, one at a time failure. After #3 I changed all the coils and problem solved