I'm getting code 231 and it says too lean or toos rich (at part load) what does that mean at part load? There are no air leaks and fuel pressure is about 43psi. and rests at 50 psi. This is a non turbo, It starts but takes awhile and then it will run for about a min. then starts to miss and gets worse untill it stalls. It will restart but without keeping it about 2500 rpms in drive it will stall. Could this be a ecm problem or just a bad 02 sensor?? Help wasting time and $$