zmm77

Hey Everyone,

I have a 2020 GLC63s Coupe with 23k KM on it.
it’s been driving amazing ever since I’ve gotten it with 0 km. I usually always drive it on S+.

8 months ago I put the Renntech ECU+ and it unlocked the extra power and it was driving just how it should.

I then installed an Eventuri Air Intake 5 months ago and there were no issues.

I added RedStar Catted 200 cell Downpipes 2 months ago and there were no issues.

You could really feel the power from the combo of the 3!

Recently all of a sudden, on cold starts sometimes my car within 5-10 min, at a traffic light, the rpm would start dancing up and down. And then the car would feel like it’s stuck and wouldn’t go above 1500-2000rpm. (The issue would go away after a few min). I kind of ignored it.

It would be unpredictable it comes when you least expect it, and sometimes it doesn’t happen at all.

It’s gotten worse now and I have had 3 CEL now.

The 1st CEL, the car was stuck like that for 10-15 min until I went back home.

I took it to the mechanic, (The report is attached).
Coil 5 had an electrical fault among other things. So I changed all the coils and spark plugs.

Car was fine for a few days and then I got hit with the same issue and CEL came on again. (Report attached) Bear in mind these are completely new coils.

It said: Coil group 1 electrical fault, Coil group 2 as well. Combustion misfire, misfire cylinder 1, 5, 4, 6 and 3.

We went for a spin with 2 mechanics and the OBD scanner plugged in to read the data while driving. Going full throttle on S+, trying stop and go, comfort mode etc. But the issue didn’t arise.
and nothing came up on the scan reader.

The mechanic said that it can’t be from the coils and it might be the Renntech ECU and that I should reflash it back to stock and the issue would disappear

Car was fine for 4 days, I thought it must have been the Renntech ECU since I’m now on stock and no issues. And then all of a sudden yesterday, car would shake and not go above 1500-2000 rpm and I got a flashing CEL.

I don’t know what to do, what would you guys recommend?
I love this car, incredibly fun but this unpredictability is really frustrating.


First CEL

2nd CEL