OK heres the setup:
04 GTO LS1, Stainless works LT's, K&N CAI, otherwise stock.
Just got the headers in this weekend. After a snafu with not getting the O2 sensors completely plugged in, the car is running good and sounds awesome.
Now, I am trying to tune it with HpTuners. I no expert, but im no noob either, I understand the basics, MAF and VE table and all that. But something is cornfusing me. I do a 20 mile run or so, logging LT's, and updating the VE table. First two times I did this, made huge improvements in the cars performance. But, even after those two times, I take the car out and log again, when I am "in the throttle" LT's look good, but when I cruise or am at idle, they read thats it lean by 10 points or so. So I updated the VE table again. LT's show lean again. Keep doing this like 3 more times. Im thinking to my self, this CANT be right. This morning, after my last tune last night, the car bucked a couple of times, which suggests the tune is off pretty bad.
Could I have ruined my O2 sensors (or got em out of whack) by running the car for a while with them not plugged in correctly? I am showing a MAF code (peformance) so I know I need to retune the MAF, but I wanted to get the speed density tune down before I did that (MAF error frequency is set to 0)
Or, is it possible that the headers somehow screw up things so that at low exhaust temps/flow, the O2 sensors are not accurate anymore?
Any thoughts would be appreciated.

FYI - I was real careful with not touching the sensors, and they have 9K miles on them.

Edit: forgot to add, I have a LC-1 WB02 going in tuesday....should I hold off till then, get some more accurate numbers?

Edit 2: I have never turned off Power enrichment before, could that be the issue this time?

Edit 3: LOL sorry for all the edits, but maybe some other tuning beginners will find this useful. After some searching it looks like I do need to turn of PE. Its probably screwing up my LTtrim values, causing my confusion.
Ill start from a good known bin file, and be sure to turn of PE.

 

Tuning via LTFT's at idle or near idle conditions with long tubes will cause you to chase your tail. The O2's don't stay hot enough and the PCM doesn't react well. At cruise it shouldn't be as bad, but idle will be erratic. Your best bet is to drive it hard for a while and get the O2's nice and hot before you try to tune that way. Or go the WB route.

 

Thats good to know. I thought as much, but I think my biggest issue is leaving PE on. Ill get that turned off first. If I still see weirdness at idle/low throttle ill just leave em be. Running lean then is no big anyways.

 

PE has nothing to do with idle or low cruise. In my
experience it -may- step on other cells depending
on how PE overlaps with closed loop areas (do not
know why, but have seen PE changes alter trims).
Look at your fuel trim cell boundaries w/ RPM and MAP
and see whether you have all 16 "in play" or have
some setup where half of them will never be hit
(like some years of F-bodies). There is no good reason
for more than one FTC to be wasted on always-open-
loop operation (MAP, TPS > PE enable). In the other
direction since low speed, low power operation is
known prone to mistrimming you probably want finer
"coverage" of the low RPM, low MAP space so that
what sucks, sucks over as small a span as possible.
You don't want off-idle mistrimming to step all over
cruise and like that.

At any rate, turning off PE entirely is going to be a
very unhappy experience for you. Potentially unsafe,
certain to push you into low-octane-table with the
ping you pick up.

I don't know whether GTO front O2s might be plug-
compatible (like F-bodies) with the 'vette rear O2s
but if so, or if willing to remove pins & swap connector
bodies, this would help the heat situation. So might
wrapping the headers (stainless is a very emissive
material, aluminum tape or a more sophisticated
wrap might help you though it's ugly).

Running lean at idle is no biggie, except that the PCM
will go over the top trying to compensate and then
every time you go WOT from idle you will carry big
bogus enrichment, losing power and making stank.

Since it's a thermal problem your best bet is going to
be a thermal solution.

 

Thanks for the additional insight.
The headers are coated, for what its worth. I won't wrap em. Front O2 harness's are different than the rears. Since ill have my WB 02 setup in a few days I might just wait till then, and then I should able to confirm if the stockers are working ok or not.

With PE off, ill be real careful on watching knock. Also, I copied high octane over to low because with the MAF disabled you drop into that table.

 

That is my next step after upgrading my front O2 sensors to the C5 rear sensors... I just ordered a set of the Denso rear sensors ($$$ ) to replace my front sensors. I got the harness adapter from LG. If the new sensors do not fix the lazy O2 switching I guess I am wrapping my headers....

 

FYI - I fixed it by calibrating my MAF. OS2 sensors are fine.