1998 bmw 318i -p1174 need help

Question

after all i went throw changing cvv and spark plug&O2 SENSOR OEM&check for any leak i can not find any ..air filter is new the disa valve i take it out clean it and also mass flow sensor i did buy new one after cleaning the old one start throw mass air code so i replac it no more air flow code oil and filter change .....it drive me mad the car it drive excellent i feel the engine have slight viberation not much idel is fine ,i took the fuel injector plug sepratly to see if it is working ..all of them are .... i did stop at a shop and the guy was looking at the same places and he can not find any thing even no matter i do bmw driving cycle i still have 4 moniter i can not set..the last thing i catch the live data
stft: 0.7 or zero or (-1.5) all at the same time changing while the car idal
Ltft :3.9 stay the same
idal:798or 800 or 817
please i need help thanks in advance

Answer 1

P1174 Fuel trim limits exceeded.

As long as both short and long fuel trim added together does not exceed 10, or total  of 10 you should be good, For now use a vacuum gauge, you will test for a slightly plugged catalytic convertor or exhaust sytem.At idle the vacuum gauge should be at 18 hg  to 20 hg. Bring the RPM up. around 1500 to 2000 RPM. iA good vacuum will go to 0 (as RPM holding) ,the reading should go to  18 or 20. A slighty plugged exhuast can cause P1174. and random misfire,and it does not even have to code up for a misfire.