Misfire cause


New member
West Yorkshire
2016 Golf GT Mk7 150
Just after other people's opinions here. Vehicle is a 2016 MK7 1.4GT 150 ACT (CZEA engine)

A couple of months ago when accelerating hard my vehicle didn't shift up a gear and engine was revving fairly high. At that moment Check Engine Light began to flash. I backed off the throttle and within a few seconds the Stop - Start Error message appeared. CEL stop flashing with a couple of minutes, but Stop - Start Error continued for the second trip I made, then disappeared after that.
I thought I'd buy an OBDeleven to try and find out what caused this "one off" issue.
I got misfire errors for all cylinders, but none recorded on the "misfires per 1000 revs"
I tried to repeat the scenario that caused the issue and again my car seemed to get stuck in gear and I backed off the throttle (but not as soon as before). This time there was no Start - Stop Error message, but OBD did show 1 misfire per 1000 on one or 2 cylinders (along with my misfire readings increasing on all cylinders) and CEL flashed for about 2 mins.
The third time this occurred, instead of letting off throttle, I manually changed up a gear, so I know the car wasn't physically stuck in gear.
After reading some posts re: Start - Stop Error, I took car for a long run to try add recharge the battery and it did seem to help.
The car only has this "stuck in gear" symptom when driven very hard and only intermittently.
I ended up booking car in at an independent VAG specialist. On his diagnostics it came back with same error codes and he showed me what VW recommend, which is for the intake valves to be walnut blasted clean. He does have the machine for this and did not charge me for the diagnosis.

Sorry for detailed explanation above, I just thought it would be handy to have all the details.

My main question is -
Would multiple misfires on all cylinders WITHOUT any other error codes likely be due to carbonisation of intake valves?

My other thought was, could it be an issue with EGR, or would I be likely to have an error code?