Hyundai 1.6t GDI high LTFT. Stumbles. Poor performance

Greetings! I'm glad I found your forum! Your videos have taught me so much!

I've got a 2019 Hyundai Elantra GT N-Line AT

Since the day I brought it home, it's had an issue with inconsistent performance, stumbling at partial throttle, sulfur smell on highway on ramps, etc.

The dealer has been basically useless because it hasn't thrown a single code. No stored codes. No warnings. It's been in no less than 20x for the issue and occasionally runs properly, especially around certain temperatures (usually around 35f). They have replaced coils and even went as far to replace the entire transmission with no improvement.

One thing is, the car runs best after a computer reset, then slowly gets worse and worse as time goes on.

I've bought various scanners and scopes. Although my initial thought was bad coils or plugs, scoping the coils shows the ignition system is working properly.

The scanners seem to show no issue with the oxygen sensors and when the car isn't running, the MAP shows what seems to be normal atmospheric pressure at sea level.

The only thing I can find that's peculiar is my LTFT. At idle, it usually hangs around +15-20% and drops to about 6% when driving.

At this point I'd rather drive the thing off a cliff then take it back to the dealer and have them tell me there's nothing wrong one more time.

There is also a small community of folks on various forms with the same issue that remains unresolved.

Any of your infinite wisdom that could point me in the right direction would be much appreciated!

Here's some screen grabs from torque pro:

I don’t have any expertise in the way of turbo setups, but I’m dealing with a slightly similar issue where my Lexus will run fine after a reset and gradually get worse. Lately I’m suspecting the MAF plug itself is either corroded or not tight anymore, because when I mess with it the computer will even out the fuel trims for a while.

It’s worth a shot. Unplug and re-plug your MAF about ten times and then see if your fuel trims change at all. In my case the short term immediately starts trying to cancel out the long term. Then it’ll settle back into a pattern of being way off until I mess with the plug again.

Wish I could offer more.

I'll give it a shot once I can even find em. I think, if it's like other hyundai 1.6t's, that there are 2 MAP sensors. One is on the cold side that only measures temp and one somewhere on the hot side. I sure hope that there isn't corrosion. The car is only a year old