On my 04 cav..

When I'm driving my fuel trim looks good, but when I let off the gas pedal the long term fuel trim goes anywhere fro. -10.9 to -14.4. Whenever it hits -14.4 it goes from closed loop to open1. When I start accelerating again the fuel trim goes back to normal. At idle the fuel trims are good.

Also I'm noticing that my back bumper around the exhaust is starting to turn black

Is your check engine light on?

Your numbers aren't really that bad. It wont set a lean/rich code unless it is -25% or +25%


- 2004 Cavalier - 124k, owned since new

Sorry it took so long to get back to this post.

My CEL isn't on but my long term fuel trim at idle is around +12% to +15% and my gas mileage sucks. Also earlier for a few minutes my short and long term fuel trim were around +14% each. When everything is all good with my car I usually get 300ish miles when I have a quarter tank of gas left. Now I'm around 250 at a quarter tank left.

When I'm driving on the highway my fuel trim numbers look good. I guess it's when I'm stuck in city traffic that my car is getting unusually low gas mileage.