misfire, rough idle disappears when engine is turned off and back on
 

Hi - new poster here. Here is my issue with a relatively new to me w208 clk55. I know there is a separate forum for this car but there is very little traffic over there so I thought I try my luck here since it has the same m113 engine like the 430 has.
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

An air intake leak?

thanks Serndipity - my MAF elbow was pretty wobbly and I fixed that with new seals, I have not looked at the throttle body yet but have ordered the o-ring that will go in there this weekend. The MAT sensor vacuum line seems ok. Doing a search here, somebody fixed a rough idle by replacing fuel vent hoses in the back - 'have not looked there yet but know that my evap canister is likely blocked 'cause putting gas in the car is a hassle.

I'll report back but figure due to the issue disappearing when engine is turned off and back on it's rather electrical than vaccum related

If your gasoline tank isn’t venting properly, here is a link that explains how the evaporation emission control system works, including options to repair, that will enable you to fill your tank.

https://mbworld.org/forums/clk-class...ease-help.html

My understanding is that evap issues (e.g. blocked charcoal canister, forgetting to put the gas cap on etc.) may throw an emissions related CEL, but do not store an ECU fault condition (DTC , which won't affect engine performance.

However, note that the fuel pressure regulator is integrated into the fuel filter and if it's clogged, could be the reason for all those fuel trim DTCs.

I realize that you aren't getting codes that apply to this but it sounds like a bad coil pack.

Doubt it's a bad coil pack, because the fuel trim is an issue in both sides of the engine (e.g. banks 1 and 2).

Considering all 4 fault codes with the symptoms mentioned, sounds like the EGR value is stuck or the pipe that goes into the manifold is clogged.

thank you derek and serndipity - I had thought of a bad coil pack as well that would normalize with an engine restart and was trying to look up how to best test coil packs - borrowed a fuel pressure tester as well and will try that tonight just in case my issue was fuel supply/pressure related

my EGR valve looks almost brand new but then the car is new to me so what do I know - I'll test that with my little vacuum brake bleeder pump later tonight

"...or the pipe that goes into the manifold is clogged." - ok, haven't poked too much around on the back of the engine - I did replace the breather hoses (they cracked when I took the old ones off) and had taken off the valve covers to clean them inside and clean out the tiny breather holes but I will check the EGR valve pipe you mention

thx much both for now

the car is testing my patience a bit, I replaced the old alternator because I had the flickering instruments lights and the alternator looked ratty and old and put an original remanufactured Mercedes one in there (scored on ebay). Had to change the connectors on the back since they were different and now I have an alternator warning flicker up on my instrument cluster every 5-10 minutes for a few seconds ..... frustrating !!

made only little progress today -work is too busy to do much troubleshooting: checked fuel pressure and it looks good (first pic with engine running) - however it doesn't hold pressure for very long - second pic is 10-15min after shutting off engine

also noticed that engine tilts/rocks quite a bit left to right so maybe my motor mounts could use replacing ....

https://cimg3.ibsrv.net/gimg/www.mbw...4cc1aa4eef.jpghttps://cimg7.ibsrv.net/gimg/www.mbw...d4678cc875.jpg