That's gotta be something else.... Why is your car running pig rich?? Even for most f/i that's pretty rich, and n/a that's a real problem. Are you getting any dtc's (probably generated by upstream O2 readings) that would back up what your afr says?
Unless maybe it is an incorrect reading?
Anyway, if anything a larger plenum/tb would cause it to run a little leaner, theoretically. And I haven't set the two down side by side to compare, but I would bet $1 that the plenum/tb on all 96-04's remained unchanged.
Thanks for the response. Long story short, I've had an ongoing struggle getting my car to run right ever since trying an aftermarket TB and 2 different plenums (with an updated tune from Bama). After a ton of troubleshooting, I was able to determine the plenum being the likely issue, but by that time my stock one had gotten thrown out
So I have a low mile stock one from Ebay that looks clean and correct, and shortly afterwards installed my AEM. However I'm guessing if there's any difference between my original stock plenum and this one, since I've reverted to that original tune, and seemingly the only difference should be the "stock" plenums.
What kind of A/F ratio gauge are you using? Where and how is the sensor placed in the exhaust?
I am using an AEM Uego 30-4100 with the Bosch sensor. I have the sensor in the back passenger O2 of my O/R Prochamber, which I understand can cause long-term condensation issues for the sensor. But so far it seems to be working reasonably, at idle warmed up, the reading bounces around the mid 14 area, and bounces around that area or a little richer in light driving. But the instant you give it WOT, it pegs 10 and stays there while you're on it.
I'm on the fence between seeing if Bama will give me a slightly leaner version of my current tune (I realize that's a liability risk for them) or saying screw it and running to the local dyno. Thanks for the help and suggestions, any advice is appreciated.