So i installed my AEM UEGO wideband today.. and well lets just say im really not happy with the results... i knew i had a miss but i was hoping it was a wire/plug related thing.... but instead i think it might be lean miss...

my idle AFRs are so lean to were the wideband cant read them (18+:1)
and at WOT i get about mid 13s to low 14s in second gear
Third gear is a better with high12s to low 13s and First is just too bad to bring up....

What i have is a 88 gm truck 350tbi on a 90 camaro RS that had a 305tbi (i bought it that way) WELLLL my guess is the previous owner didn't bother changing any of the Fuel Mapping from the old 305 tables.... and with a MAP sensor that means the added displacement wont be read by the computer so it wouldn't know to give more fuel... right?

Also the headers were swapped to a set without an 02 sensor hole. i know in some cars this can make the computer revert to a really safe AFR map and timing But it wouldn't be making the engine run lean would it?

Well this sucks because right now this is my daily driver, i planned on switching to carb in the summer, should i just bump those plans up so i can tune it myself?

A miss will send unburned oxygen out the tailpipe, and the o2 sensor will show lean.

I think if you get the O2 sensor working it will make an improvement. It does most of its work at part throttle. I've also seen a miss on the O2 sensor side of the engine lean out the rest because of the unburned fuel getting into the exhaust.