If they're negative, you're running rich which means the car is putting more fuel in because of some imbalance.
If its positive, you're running lean where its putting less fuel in and allowing more air, this could cause engine detonation if it gets out of control.
I scanned Mike2005's car a wihle ago, his long term trims were about -10%. Mine on the other hand, were about -24% which caused me to get CELs due to running too rich. I have since gotten a tunable MAFci from CPE and I tuned it down so its closer to 0, no more CELs.
Also, running rich will produce extra soot to show up on your tail pipes, so check for that.
At idle, my short terms are at 0, same as when I'm at speed. Long term trims on the other hand, are +20.3 at idle, and between +5-10 at speed.
I'm just trying to figure out why my Catalyst Monitor is showing as Not Ready. It's the only emissions monitor that shows as Not Ready. My cat temps are around 1500 degrees, and I read that they're supposed to be around 1200. I thought maybe my car was running rich, and that's why the cats were hotter, but I guess not.
I think I need to use a visual oscilloscope thing to read the O2 voltage, 'cause it's hard to visualize it just using an AutoXray. My downstream sensors seem to fluctuate at the same speed, or slightly slower than the upstream ones, and I read that the Catalyst Monitor uses a cross check ratio b/w the up and downstream sensors to determine the cat's efficiency.
I don't understand why the cat's wouldn't be working, I just got my y-pipe replaced by Kooks at the end of August.