Okay so last post I was having troubles fixing my g35 so this Friday and Saturday, 500 dollars later I have a torxe stainless steel exhaust system installed in my g35, last post I was having trouble fixing my o2 sensors or upstream sensors I think their called. I was able to replace it all with going to a local part out and getting what I need for a good price. So after fixing all that I was expecting my car to run better and smoother but it still runs just as rough. But with plugging in the upstream sensors the computer is able to read codes properly unlike before so it kept telling me I was having misfires in 2 out of my 6 cylinders so I pulled each coil pack one by one and replaced which ever one needed to be replaced. After all that I was able to fix misfiring issues but the car still runs rough and I get a code called p1148 closed loop, the car just doesn’t seem to be timing it’s self I tried a ecu reset but doesint work and I clear the codes but the check engine light comes back on after 5 mins of idling and the idling is really rough but it runs and drives better just not quite stock and that’s what I’m looking for. Need guidance. What steps should I invest into next and ask questions to learn more be glad to answer... struggle bus.

 

Well P1148 means it's just bank 1 that's having problems. I'd double check the harness and inspect the wires and make sure nothing is melted. If it wasn't plugged in that means the harness was just dangling and it could have gotten onto the header and melted part of the wire.

If you used an old O2 sensor it's also possible that it's just damaged.

EDIT: If cash is a problem you can try cleaning the O2 sensor. Remove it, get a glass jar, put a little fresh gasoline in it, just enough to submerge the part of the O2 sensor that's inside the header. Secure the harness up so you aren't getting any fuel on it. Cover and let it sit for 24 hours. Then take the O2 sensor and swish it around a little in the fuel and you'll get a lot of carbon that will shake out of it. Remove from the fuel, let it fully air dry, reinstall, fingers crossed.

Sometimes it works, sometimes it makes the problem not quite as bad, sometimes it's still bad.