Seat Leon FR 1.4 TSI ACT

[krimp]

Hello, i'm new here. I have a misfire problem with my FR. First let me give you a little background about the car. It is 2015 MY, it has 79k km on the odometer. Since covid it has not seen much road - last three years only 12k km total.
I bought it second hand in 2019. and i maintain it regularly. Since the beginning the idle was a little rough but i did not pay much attention to it. In 2020. i changed the spark plugs and basically there was no improvement with the idle but i payed no further attention because i did not notice anything else - no performance issues, no fuel smell, no starting problems...
Today i checked advanced measuring values in VCDS and i was very suprised/shocked to see that number of misfires for cylinders 1 and 4 was 35k+ and for cylinders 1 and 2 was 12k+. I do not know if that is the total number of misfires since the car was new. I left it there idling for a bit and the number of misfires was increasing, even when i gave it some rpm it was also increasing. I will add that there are no faults when doing the autoscan.
Does anyone have any thoughts about this?
Thanks

 

[Mr Pig]

I have the same engine. The slightly rough idle seems to be normal. My car has always done it and no servicing or plug changes have cured it. It's so slight I don't see it as an issue. Maybe yours is worse?

I'm not aware of ever having a misfire. I would suspect the usual things like plugs, leads, coils etc. Process of elimination I suppose. Did you fit the correct plugs? Has the timing belt been done and by whom?

 

[krimp]

Just to be on the same page, i think i have a misfire problem - judging by the vcds readout. According to what you described we basically have the same experience with the rough idle - it is by no means alarming, it is very slight, it's just a little judder here and there. That is the exact reason i never did anything about it. Also taking into account that there are no performance issues of any kind i am inclined to think there could be an error with the log. Seeing that there are no other issues with the engine aside from slightly rough idle (i also do not see this as an issue, i was just surprised by the readout) nor with the rest of the readouts like O2, injectors and eco stuff it seems chasing gremlins would not be the best way to spend time/money trying to find the possibly nonexistent issue.
The plugs were changed at the authorized service so i guess they put the correct ones. The timing belt is the original one, it has not been changed yet.
Thanks Mr Pig

 

[Mr Pig]

According to what you described we basically have the same experience with the rough idle - it is by no means alarming, it is very slight, it's just a little judder here and there.

Yes. To be honest I don't even notice it unless I'm actively looking for it. Car has to be quiet. I think it may be an artifact of the ACT system but I don't know.

If the timing belt is ten years old you really want to change that. It's expensive unfortunately but ten years is well into the land of dragons for a timing belt.

Another possibility is intake fouling. The engine is direct injection so the fuel does not wash over the intake valves. Which would not be a big deal were it not for the crank case breather dumping crap into the intake! The intake can get gummed up and cause issues. Worst case the valves can stick open and kill the engine so it's best to investigate issues rather than hope for the best. I suspect that if the log reports misfires you've actually had misfires.