Alright I have given advice on this issue for a couple other people but now I have actually run out of tricks. I have a 99 z71 with 04 motor but is dressed out with all the 99 stuff. I have had this motor in there for about 2 and half years now. I had a vacuum leak about a year ago and figured that out by spraying carb cleaner and found intake manifold bolt seal was blown out and random miss fire went away until the other day.

When driving it runs good no problems. At idle after motor is heated up most of the time i will be driving just fine but when i come to a stop it sounds like my truck is barely hanging on (almost loping). It misses real bad and i got my codes ran and i got: heated 02 sensor, fuel ratio off, random misfire. I don't think 02 sensor because when it starts running really rough I can smell the gas so I am sure thats why that tripped but I don't know. I disconnected maf sensor and truck bogged down for a second and returned to running like crap. So I'm back at vacuum leak but I can't find one. My step dad suggested intake manifold gasket so I will give that a try this weekend.

I need to get this figured out because I don't want to drive it with it missing, but its my daily driver and all I got. I would appreciate any help or if you know whats going.

 

I would replace the O2 sensor reset the ECM and see what happens.

 

you think the 02 sensor is my problem? do you know which one is the heated 02 sensor?

 

Update on my truck, I did the intake manifold gasket and mass air flow sensor, but nothing really changed. I knew my back 02 sensors couldn't make my truck run bad, but the front could. Come to find out, my 02 wiring harness had decided to come out of it clips and get real nice and close to my exhaust and melted all the coating off the wires. I fixed wires and she runs like a full bred racing machine. Ill put it to you guys this way, my truck before was being a diesel and rolling coal out the tips when i revved it up with it running so rich.