Goods days,
2014 Hyundai Elantra GT
1.6 Gamma engine with 6 speed automatic transmission
current milage: 103k miles
transmission fluid changed roughly every 30k miles (last time at about 90k)
fluid level within specs, doesn't smell bad and the color is slightly darker than a new fluid.
I bought the car new in 2013
my car has mostly seen highways pretty much all the time, 2 weeks ago I got stuck in a back to back traffic for about 3 hours, since then i've got some weird problems.
the first one is if I stepped on the gas a strong kick happens at downshifts like i got rear ended, this happens if I was slowing down to take a sharp turn then tried accelerate again. It more obvious when shifting out of third gear. this problem appeared earlier but it happend once every few moths, but now it happens everytime i step on the gas.
the second one if I go full throttle the car will short shift at about 4k rpms and sometimes will alternate between two gears, this happens from 4th gear onwards.
what could be the problem?
Your transmission is on it's way out. Those cars literally fall apart with age and at 100k+ miles, it is due.
I would start looking for a replacement vehicle before it totally goes out.
A few years ago a guy that owns a transmission shop told me that he could buy a brand new transmission from Hyundai for a thousand bucks. Probably not true anymore but you might want to call around.
Since you're the original owner you are just barely out of the 100K warranty period. It might be worth seeing if Hyundai will do anything for you. (Probably not, but it's worth a shot.)
Your transmission is probably worn out. It helps though to research the characteristics of that particular transmission. It's possible that a non-fatal issue could cause a problem like that. Does the transmission work OK if you shift it manually?
I had a similar problem years ago with my daily driver Saab after driving it on one of the most horrific roads on the East Coast, the infamous BQE (Brooklyn-Queens Expressway). After hours of crawling in horrendous traffic and dodging accidents and broken-down vehicles I found that the automatic transmission's shifting had become erratic, but manual shifting worked OK. This car has a ZF 4HP18 transmission, and it will develop that symptom if the governor seals deteriorate and leak. The seals are pretty easy to replace and can be done with the trans still in the car, so not a big deal but to the uninitiated it appears the transmission is shot. (Back when those cars were more common you could pick them up cheap because the "transmission is bad", spend a few dollars and an afternoon replacing the governor seals, and drive it for years or flip it.)
Of course your car is completely different, that was just an example of a symptom that is not as bad as it appears to be. So while it is likely your transmission is toast, it's worth finding out if there's something relatively simple that might be causing that symptom like bad shift solenoids, bad sensor, maybe a bad electrical connection, etc. Unlike my car whose trans is hydraulically-controlled, yours is computerized and you need a good independent mechanic with a fancy scan tool like Scotty uses to analyze the data.
Then if you can get it working relatively easily and inexpensively I would dump that thing because as has been stated that car is at the point where it's most likely going to fall apart and become a money pit.
