Finally got a quick scan today and I'm getting a maxxed out reading of 16.38% for long term trims. The guy who was doing the scan for me suggested a vacuum leak was present. Also its throwing a code (I thought this was because I didn't have a rear o2 spoof for 3 days) saying I'm running too rich on bank 1. I believe code P140 or 171, but I'll update this thread when I run outside into the cold dark night to read what I wrote down.

Anyway, anyone have an idea of where a leak could be or what could cause such an awful reading?

Few things that you should know:
1.) I set the idle screw to a voltage of .71-.72 when doing the TPS enhancement, but never had a CEL thrown at me.
2.) This light showed up AFTER headers
3.) Rear o2 not being plugged in for 3 days?
4.) Front o2 going bad?
5.) Replaced/repairs all T-fittings and in-line fittings on the vacuum line that goes all around the SC.
6.) Boost gauge will sometimes flutter up from -10 to about -7 when slowing down from a cruise (usually going into a small town from 65mph to 35mph).

What should I start with? I have a feeling I could gain some performance back once I figure this out.

Make sure none of the cables in the back were cut when you did the headers. Look at the wires to front 02 especially.

140 is no activity from rear 02 (ok if its disconnected)

171 is Fuel Trim System Lean

For 171 check the following:

- 02 Wires (mentioned above) make sure they are NOT touch the headers.

- Poor PCM to engine block grounds

- Fuel pressure

- Fuel injector fail

- Bad PCV

- Vacuum leaks, check the throttle body and EGR

- Exhaust leak (likely) Outside air can be pulled into the exhaust stream before teh 02 sensor (IE from the a leak in the headers) causing the 02 sensor to read a false lean condition.

- Bad MAF Sensor

- Fuel contamination

If you have a scan tool you can check for vacuum leak looking at the Idle Air Control parameter. If its more then 5 then you may have a vacuum leak or a problem with the Idle Air Control System.

Yeah its Code 171. Code 140 never came back after I put the rear o2 spoof in and had the codes cleared.

Lets cover this one by one:

o2 wires: For the front o2 I assume and you suggest maybe one of the wires was cut or touching the headers?

Poor PCM to block grounds: where do I start looking?

Fuel pressure: What would cause this to change recently?

Bad PCV: Just replaced it, but didn't install a gasket. Yes there was a PCV paper gasket between the SC and top plate. I didn't find the logic in hunting one down...this a possible issue?

Vacuum leaks: Where on TB and EGR?

Exhaust leak: The flexpipe ticks, but thats true with all SLP headers. Bad weld or need to re-tighten and check gaskets?

Bad MAF: Way to check?

Fuel contamination: How and what to do?

Lots of questions for ya big man, in the meantime I'm going back out to mess around some more.

I would start here as this is the most suspect. Recheck the torque settings on your header bolts where they are connected to the heads. The exhaust leak if you have it will be BEFORE the 02 sensor so its not the normal flex tick from the headers. Also check your crossover bolts and make sure the flanges are tight on it.

for fuel contamination, run it as close to empty as possible and get a fresh fill with gas from a different station than before. Would a new fuel filter help?

SLP torque specs were 22ft/lbs right? Don't have the paper handy.

I'm gonna re-torque when I can.

http://www.3800tech.com/lists/torquespecs.html

I went through the bolts and made sure they were TIGHT, nothing insane, but we tightened more than 22ft/lbs the first time. However one bolt in the back was short and this confused us when we originally ended up with an extra stud. I took this bolt out of the rear header and notice that normal than 2 threads were actually in the head, so I duck into the box and found the extra stud. I put this in its place (which was probably the original one, but by 11:30pm you don't care as long as the bolt fits). I also took the EGR bolt out that connects the tube to the headers, and I retorqued that one to spec (18ft/lb). Started car up and check engine light is still there...I doubt it will go away.

What else could it be?
Crossover clamps are tight.
Original O2 sensor threads were striped, but we used a lot of anti-sieze and put it in the headers...so maybe I'm getting a leak there. Would a bad o2 cause the long term trims to go out of wack?
One of the vacuum lines on the TB was disconnected when we first finished the headers last week. It was the middle one on the "tree" on top of the TB and the car idled poorly until we reconnected it. I traced the vacuum line back and it appears to go into a wire harness loom. Any idea whats in there? Maybe a leaky fitting?

What else should I check for? Should I try putting a little soapy water on the headers when they are cool to see where it bubbles?

This is driving me nuts!

A bad 02 can certainly cause it. You need to find a scan tool so you can check your IAC counts. This can tell you if its vacuum related and let you concentrate looking in the right place. The LTFT can take a bit to sort out so the SES may not go off right away if you fixed it with the header bolt. You can disconnect your battery for 30 min to reset the pcm and if it comes back on you know you still have the hproblem.