Hi - new poster but long time reader. Here is my issue with a relatively new to me w208 clk55 m113. Car has the following codes and CEL is on:
P0400 EGR
P0170 fuel trim
P0173 fuel trim
P0100 MAF circuit
and the following issue/s:

- rough/fluctuating idle, engine sometimes dies when coasting to a stop
- occasional misfire, CEL light blinks and car runs rough, no power, smells of unburned fuel
- also when putting tranny in park after a drive the rpms rise to 1200-1500

the misfire occurs maybe on 3 out of 10 drives, if I stop, turn engine off and immediately back on the misfire disappears and the car runs perfectly fine

the rough idle is also somewhat intermittent - it's never "glass smooth" like I find Mercedes V8s normally to be but it's reasonably stable when it's not acting up

the car has new plugs, wires and MAF including elbow seals, I replaced the upper breather hoses and cleaned the inside of the valve covers.
The vacuum lines that I can see look ok and since the issue disappears after an engine restart I am thinking my problem is electrical and not vacuum?

Any ideas where to look next ?

thx much All

2002 CLK 55 w208

Try to find a more detailed description of the codes, this will offer more clues.

RE EGR what type of failure ?

Fuel trim, long or short term ? Lean or rich limit?

MAF, high or low signal output ? shorted to ground or voltage? Open circuit?

I'd hang a volt meter or scope on the MAF output and watch it for an out of the ordinary voltage.

A hidden gem. On my 97 SL320 and 97 C280 With a M104 inline 6 and Bosch ME 2.0 / 2.1 compuer, if the computer detects a miss fire, it shuts fuel off to the miss firing cylinder. Your car might do the same. This slightly complicates diagnosis as an ignition fault will look like a fuel injector driver fault.

This is exactly what also happens on M112 and 113 - the misfiring cylinder will be shut down in both fuel and spark to prevent cat converter damage.

to OP.

have you checked the spark plugs - my old W210 used to do this when I bought it, the plugs were bad, once I replaced all 12 it never misfired again.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

The first 3 codes can be caused by a variety of things as has been suggested. The P0100 is a little odd (I've never heard of it). Did you replace the MAF yourself? Is it OEM? There are a lot of cra* MAF's being sold for cheap. A lot of cheap parts work perfectly fine, but often not cheap sensors of any kind.

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra