(posting here because the cls forum is alot quieter and havent had a response yet so hoping someone here might be able to help since they are similar cars) Hey guys, so to give some context i'll explain the entirety of the situation im facing...

I had a couple of issues with my 2011 (2012 year in the states?) cls63, the first one was that on accelerating the engine would rise and lower its rpm as if it was confused as to what gear it was in and felt as if it was shifting up and then back down without actually changing gears, i had a mechanic look at it and attempt to fix that issue and he suspected the transmission valve was at fault, he from my understanding did a refurb job on it and gave it a tune and that basically fixed that 90% it was still subtly doing it on the change from 3rd gear to 4th gear. About a week or 2 after picking it up the issue was returning and progressively getting worse again and since picking it up i had noticed something else which is the main issue i now have.

The car seems to surge in rpm randomly, i usually note that it does this 70% of the time in the morning when i first turn it on and it runs its cold start, while reversing it will surge in rpm and create enough power that the entire car will basically jerk in gain/loss of speed/power. i'll have a video attached so you can get a better understanding.... this same surge will happen randomly albeit less frequency than ive noticed when reversing, while driving and coming to a stop it will do the surge, sometimes if you just move like a meter forward without touching the accelerator and letting it move on its own idle speed it'd jolt/jerk that way and then get itself together. so it'll only surge like for those few moments and then its fine until it decides to do it again randomly. i've given it to my mechanic again but i just picked it up from him today because he cant seems to recreate it or it hasnt failed for him...

one other thing to note about a 3weeks ago, coming from work the car had surged while reversing and my put was lightly on the accelerator and the car stalled. when turning it on again i had a check engine light which i had an assumption it might be because it stalled it mightve had to much fuel in, the two codes i got was:
P2097 - Post catalyst fuel trim system too rich Bank 1
P0304 - Cyclinder 4 Misfire Detected

i cleared the codes and it hadn't turned on since

Just wondering if anyone can shed some light on what could be causing it so that if i go back to a mechanic or someone else i can atleast ask them to look at a few things rather than just being told to wait for it to 'fail' and then bring it back cause im not getting any CEL's right now and i doubt i will anytime soon.

https://drive.google.com/file/d/1YLe...ew?usp=sharing (14 seconds in)

link to video of issue that i could get, it is abit hard to get while driving as i dont know when exactly it happens
the rpm surge will be at 14 seconds in (you can also hear the revs if your audio is up)

car is stock except for a res delete with straight pipe replacing it, if it matters.

 

The misfire, random surging and rich code lead me to believe you have a failing Oxygen sensor(Upstream or Pre-Catalyst). They report AFR to the ECU which can directly effect the tuning on the car in a negative way if it is reporting incorrect information. Cyl 4 is on the Right/Passenger side(left side if looking at the engine from in front of the car), so you for sure need one, but I would suggest replacing both as they are the same age and the other one is likely to fail soon.

 

I concur.

 

this might sound dumb as im not mechanically knowledgeable, would it be possible that if i got a cat delete done as i was possibly going to get one done, would the coding that they do to remove the CEL thats triggered by the removal of cats also rectify the issue? or is changing the sensors the only way

thank you guys for your help, appreciate it

 

If it is a Precat, no, you need that for the car to run.
You might want to check your injectors. You may have a leaky one which could ruin your motor if left unchecked