I have a 2009 civic, 1.8L, automatic, 280000km. Had a P0128 code but fixed with new thermostat (stuck open). I also noticed my lgft was getting as low as -15 and stft stayed anywheres whithin 1 to -10 (at idle and driving). After looking aroung, i noticed the pcv pipe was crushed and pluged, replaced it and fuel trims went back to normal. After about a week, they started going back down. Lgft stayes around -5 to -12 and stft is around -1 to -7 (at idle and driving). The car is a bit sluggish, especially with ac on. I cannot find the problem. I checked egr valve and injectors and they seem fine. I adjusted valves and it helped with ticking noise but did not change fuel trims. Any advice is greatly appreciated!
I would do a compression test to check for a blown head gasket from the overheating.
Thank you for the response, I will do a compression test and come back with the results. I must note my car never overheated (to my knowledge) since the thermostat was stuck open. It just rarely got to operating temperature😂.
negative fuel trim values mean the computer is trying to take away fuel (mixture is RICH). Yours actually don't look terrible. They're pretty low at idle. When you drive they will move around.
Did you check your air filter?
