Sabadara

Hi guys. On my 2007 CLK550 the engine keeps shaking when coming to a stop sometimes. If I stop aggressively, it even stalls on occasion. When it's idling, the rpm sits steady at first, then drops and jumps up quickly, then goes back to normal, and over again.
I cleaned the MAF sensor and the throttle body but did not make a difference.
It does burn quite a bit of oil, but I don't think that has anything to do with it. The oil change did not make any difference either.
What do you guys think might be happening?

Fatz

Some things you can check/try...
Ensure the engine cover is properly seated over the MAF housing
Check for any loose/disconnected vacuum lines
Check of have your battery checked
Use a bottle of Techron fuel system cleaner

I've had those symptoms with defective spark plug coils and ECU, but those issues also gave a CEL.

Sabadara

Thanks for your reply.

I'm sure the engine cover is on properly, and the battery has been replaced. I will check the vacuum lines and try Techron but I think the problem is similar to yours.
Even when I first bought the car, it would randomly start misfiring, and it would go away with turning the engine off and starting it again. Shortly after the CEL came on, so I took the car to a workshop and there appeared to be a problem with cylinder 2. We also found that coils on 1st and 2nd cylinders had been numbered and switched. It seemed like the previous owner had been dealing with some problem with coils, but switching them back actually turned off the CEL. The car stopped misfiring for a few months but it came back, so I decided to change all the spark plugs and also the coils on 1st and 2nd cylinders. After a few months, misfiring again. Now I went around all the cylinders with a new coil until I found the one causing the misfire. It's been like that since then, and I've had no problems with misfiring, but not it shakes and stalls.
How did you find out which spark plug coils were defective, and how can I check if my ECU is not causing this problem?

Fatz

My problems had originated from a catastrophic radiator failure and the resulting coolant everywhere and the resulting overheating. After replacing the radiator, the car started to intermittently misfire. It seemed to be temperature related. The CEL indicated shorts and opens in a couple coils intermittently. I replaced the wiring harness and 2 coils due to the direct failure of the radiator. Coolant got into the wiring and also caused a short in the #5 coil connector.

I could drive the car 400 miles without any problem, park it, restart it after 15 min and it would misfire. After changing the wiring and coils I started getting CEL indicating insufficient current for coil 5. It took me a couple of tries but finally got this ECU repair place (I would not recommend them) to check the firing logic circuitry since it seemed to me that 2 coils were apparently drawing current at the same time. I had them replace 2 logic ICs since the ECU is tuned and I did not want them re-flashing it.

If while it is misfiring you spray (mist) some water on the ECU and the problem readily goes away, it could be the ECU. In my case, when the car is moving there would be sufficient airflow under the hood to keep the ECU cool enough. When I parked, the heat from the engine and no air flowing would cause the ECU to act up. If there is a poor connection on the ECU, it could act up with temperature changes hot to cold or vice versa.

There was another thread on an intermittently failing ECU where the OP did several steps to isolate the ECU and he found a really good ECU repair resource on EBAY.

Kelvin Bellrose

I have the same sort of thing with my 07CLK550. When driving it runs smooth, but when coming to a stop it will get weird and want to stall and act a little surgy. It hasn't actually stalled yet, but seems to be getting worse. I don't drive it much because I've got the C class for the winter.
I am not getting any cel or codes of any kind. It is not misfiring, but seems like a rhythmic anomaly. Someone had a video of a 550 doing the same thing, and listening at the intake it makes a different sound for a half a second and then back to normal almost like a gurgle of some kind. Maybe it's the sound of the throttle plates opening as it counters the dip in rpm.
I've read a lot about this, and people change the pcv and maf, map, and the problem seems to come back.
Can someone explain the idle circuit, and does it have an idle pintle?

Rudeney

Make sure the engine cover is securely seated on the opening to the MAF sensor and that all vacuum lines are in good condition.

Kelvin Bellrose

There is a vacuum line that goes to the intake manifold right in the middle, but there is some kind of plastic cover on it. I have pulled pretty hard and it does not want to come off. My fingers get all black from the hose, so I am sure it's rotten. Is there a trick to unhooking the line? I don't want to bust off the connector accidentally.

Rudeney

Can you take a photo?

Kelvin Bellrose

Rudeney

Where thee white arrow points? I believe that is an electrical wire under a plastic cover.