Heyyyyyy.... for those following this in 2019 June.... almost July...
1) This is exactly of LTFTs and STFTs are supposed to function. Which means the guy who posted this thread may not have fully understood the deal with fuel trimming.
2) Here is what I mean... after detecting imperfect combustion, The Short term will start to move in either the positive or the negative % direction... taking Long term along as well.
It will keep on going until the combustion becomes perfectly sound (14.7 air: 1 part fuel). Once this is reached, the LTFT remembers the percentage value while the STFT goes BACK!! to zero(near zero)...
3) This means your engine will idle perfectly fine (although not with as much power since there is either more fuel or less as per design specifications)... however, for you sits in the ECU a vital data The LTFT... (sort of like children that wait till mom and dad get home and tell them how the people treated them....sorry bad joke).
4) So the LTFT sits there, to highlight an issue that needs to be resolved.
5) Once you solve the issue.... the STFT will start going in the opposite direction.... It will keep on going till it most hopefully reaches a point where the combustion become perfect again and the LTFT % becomes a near ZERO value... (which would mean that problem is solved.)... the happy ending is always when both STFT and LTFT are +- 5ish% from zero.