Help - 2019 gti runs rough at idle and misfires- could it be PCV?

[2019mk75gti]

Hey there guys ,
Im troubleshooting an issue right now where my 2019 gti will stutter and sometimes even die when it is at an idle for longer than 10-20 seconds and STFT and LTFT go as high as +/- 10-15% and sometimes even - 40-50% when idling so super rich.


occasionally I get codes for multiple cylinder misfire , cylinder 1 misfire and cylinder 3 misfire and flashing CEL although if u clear the codes and try to recreate for diagnostics they don’t come back.

So far I’ve only gotten the CEL 2 times however only when the car is allowed to idle for long enough to get the really rich STFT.

additionally, on the off chance that it might be the PCV valve I tried removing the oil cap when the car was running to see if there was an odd amount of vacuum and the amount of suction was so intense that it sounds like a shop vac (not just the normal amount of vaccuum)

does this mean that it’s indeed my PCV valve or are there other diagnostics that need to be done please help because I’m getting stumped.

Thanks in advance.

 

[Diggs24]

disconnect and clamp the evap line that goes into the left side of the pcv.

 

[2019mk75gti]

disconnect and clamp the evap line that goes into the left side of the pcv.

And what do I look for when doing this as far as changes in the car etc

like how do u use that to diagnose ?

 

[Diggs24]

If it is dumping fuel you will get those symptoms.

 

[2019mk75gti]

If it is dumping fuel you will get those symptoms.

Right but what does clamping the evap line from the pcv tell me ?

like what do I look for once I do that ?
Will there be an immediate change in data block values or how the idle sounds etc ?

many times the only thing I can pick up on that’s abnormal is the fuel trims being rich.

 

[Diggs24]

trims should no longer be wonky, no misfire causing cels

 

[TheMechanicDude]

Tuned?

 

[uberdot]

Reviving this. I’m getting LTFT around 15-20 while idling. Cruising and accelerating it goes near 0.

STFT ends up -25 to -30 between slower shifts, low speeds and bounces while cruising but likewise during acceleration it seems near or at 0.

At idle the STFT is likewise near 0.

I was under the impression the injectors were the culprit but from what I’ve read bad injectors would be dumping STFT at idle and heavy throttle. I cleaned the MAP sensor; it was pretty nasty. I did a couple fuel treatments (Jectron and Seafoam). No longterm difference.

 

[AceHammer]

Easy way to check the pcv is to pull the oil cap while at idle. There should be significant suction and the car should instantly start to stumble. If nothing changes or it’s blowing air out the pcv is done.

Edit - reading is hard mobile is hard lol

 

[uberdot]

Easy way to check the pcv is to pull the oil cap while at idle. There should be significant suction and the car should instantly start to stumble. If nothing changes or it’s blowing air out the pcv is done.

Edit - reading is hard mobile is hard lol

I’ve tried this and the car definitely goes into Daewoo mode. I guess I can try the @Diggs24 method but wouldn’t the oil cap test have resolved this?

 

[Drexel]

I got a 2019 Gti..i'm pretty sure it's the Vid.

Serioulsy...no problems with my Rabbit yet. Only 12k miles.

 

[uberdot]

I got a 2019 Gti..i'm pretty sure it's the Vid.

Serioulsy...no problems with my Rabbit yet. Only 12k miles.

Took about 30K for mine to start creeping in. These are fun cars and swiss army knives in many respects, but it appears most have at least one of a handful of common problems. I came from The Civic EG, a Toyota Hilux and a VR6 before this so I’m probably a bit spoiled in the reliability dept.

That said I gotta figure these fuel trims out

 

[2019mk75gti]

Took about 30K for mine to start creeping in. These are fun cars and swiss army knives in many respects, but it appears most have at least one of a handful of common problems. I came from The Civic EG, a Toyota Hilux and a VR6 before this so I’m probably a bit spoiled in the reliability dept.

That said I gotta figure these fuel trims out

For me it was my injectors that went bad at 30k. That’s for a 19 model year

 

[uberdot]

For me it was my injectors that went bad at 30k. That’s for a 19 model year

Out of curiosity, what were your fuel trims like? Were they off under load, idle or both?

 

[RisingFallens]

Not looking forward to the eventual Injector issues ):