So, I just put stock injectors in my car and went back to N/A and now I am throwing a code 51. It doesn't throw it on the freeway, only when I stop in town and am idling or starting to go. When I start off, it hesitates and acts like it's cutting out until it reaches higher rpm. Do you think it's my o2 sensor? When I had my turbo on it, I ran hella rich for a little while and the o2 sensor had never been replaced, so I think that might be it. Anyone have any other ideas?? Like I said, for some reason it only comes on with stop and go driving, never once came on during freeway driving for like 1 hour, then right when I start in town, the car won't hardley idle, then code 51 kicks in. Also, it will idle perfectly fine sometimes, then start sputtering and puff some black smoke when it sputters, (black smoke=rich)I don't get it. I got code 51=lean, why black smoke when I idle. It's all stock fuel system with no afc or anything. PLEASE HELP. Thanks.

I'd suspect O2 sensor. If the ECU doesn't get what it likes out of the sensor, it ignores it and runs a default map which is intentionally richer to protect the engine. ECU could be telling you the O2 sensor failed in this regard and just ignoring it.

Okay, I changed the uptsream o2 sensor, NOT THE PROBLEM. Any other ideas on what it might be???? I am freakin lost guys. HELP.

whens the last time you changed the fuel filter ?

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I've never replaced it, how hard is it to replace it?? That just might be my problem, I only have 67k on the car though, oh well, that's probably it. I'll try that and get back.

OKAY!! So now I have changed my fuel filter and my O2 sensor. I STILL HAVE THE SAME EXACT PROBLEM!!! I am getting sick of my fucking car being stupid. What the hell else is there to do?? Coolant temp sensor??? CODE 51 CAN SUCK MY B@LLS. PLEASE HELP MORE!!! Thanks fellas.

51 | Fuel System Lean
MAP sensor output - pull this guy out and make sure it's not clogged up?
Injector - could be intermittent sticking?
Fuel pressure - fuel filter replaced, otherwise stock system
Intake air leaks - any vac leaks?
Heated oxygen sensor - replaced
Adjust S-AFC - N/A

If it's a fuel injectors stuck, how will I know? Also, how do I check the MAP sensor, do I just take it off and look at it?? Lemme know. Thank you for all of your help.

cough cough

Did you replace the fuel filter?

Just pull the MAP and make sure it's not covered in gunk, for starters. Be careful when removing those screws, since snapping one off in the manifold would really be the suck.

As for a sticking injector, I'd wait until you've ruled out the filter before going into that. I've posted about it in other injector threads within the last month or two and would rather not go into another four paragraph response. A search will find it, I'm sure.

Yes, I replaced the fuel filter already, didn't change a thing. I have also changed the o2 sensor, didn't change a thing either. Checking my MAP sensor now, it was pretty clean when I put it back on my car a few weeks ago, so I don't think that's the problem. But thanks. Gotta link to your post for my sake?