Replacing the EIS is not a DIY unless you have SDS. The part can be had for under $400:

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There are two ways to do this, One is to order a "green" or "orange" key for your car that is basically a special programmer that will download the pre-set key codes into a new EIS. Another option is to use SDS to read the data from the old EIS and transfer it to the new one. If the EIS is dead, then the green/orange key is the only way to go, but if it is working and just giving errors, then, if you had SDS, you could DIY. It's a 30 minute job (at book rates) plus another 30 minutes of programming with SDS or up to 3 hours with the the green/orange key.

 

update: the clk550 is no longer in our possession. with so many repairs needed, and the strong likelihood that it would continue, we decided it wasn't the right car for us at this time. the car was beautiful and fun to drive, but with my fiance working full time and going to school full time, we needed for her to have a car that was more reliable. before trading it in, it died twice just on the way to the dealership. obviously this was from not electing to do the eis repair for $1k. so, we landed on a brand new kia optima for her which gives us everything we need for right now. and, when she's done with school, maybe we'll come back and see if the clk or any other model is something we can work with.

i want to thank you all for your help as it was a very frustrating couple of months dealing with this.

 

shotgun approach rarely works with MB

Better luck with the Kia