ETA Cleaning & Inspection, '94 E420 - M119

[HeathRJ]

I've been having idle problems lately - engine dropping below 500 rpm pretty consistently and even dying a few times. Based on reading this forum and JimF's website, I was thinking that the wiring in my ETA (throttle body) was shot and needed to be rebuilt.

Well, I pulled the ETA out this morning and found the wiring to be in perfect shape after opening the side cover. Even makes me wonder if the throttle body has already been replaced. When I turned the ETA over, however, I found that the underside of the plate was completely caked with carbon - 1/32 to even 1/16 of an inch in places. The intake directly below the ETA was also very caked with carbon. So I cleaned the plate thoroughly and reinstalled. This seems to have cured the idle problems as the idle stays above 500 at all times and throttle response from a stop is greatly improved. We'll see how it does with further driving.

Now for my question. Is this amount of buildup common or does it point to another problem? EGR System? Any insight or recommendations would be appreciated. Before and after pics of the cleaning are attached. First is the top, second is the underside, third is the underside after cleaning.

Many thanks to the forum and JimF for the wealth of information.