2000 Maxima Power/Acceleration Help/Fix Unplugged o2's

[jsta22]

I've done a million searches, with a good deal of help on this situation, but wanted to get some help on what I think I may have uncovered.

I own a 2000 Maxima SE with now 160k miles.. (Purchased last year with 129k)

First purchased, I replaced 6 plugs (NGK Platinum) car still developed an erratic idle, and almost stalled every cold morning, which led me to buy new coils (OEM) which solved that problem.
Purchased and installed New MAF sensor (OEM from Nissan) which helped some it seemed with power, but it would slowly go back to milder, or less acceleration the more start-ups i had and drive cycles.

I also had a New bank 2 Pre Cat O2 sensor installed by mechanic, which surprisingly made me notice a good deal of some power restored. I then replaced Bank 2, or front Pre Cat as well (Cat Efficiency code for inspection) since then, the p0430 just keeeps popping back up within 100 miles or so, sometimes less..

Pissed off at the lack of power and acceleration again, and resulting hesitant downshifts when attempting to pass/accelerate..
I disconnected the 2 oxygen sensors (Pre Cat) and to my surprise, got a Great Deal of acceleration back it seemed! The car downshifted better at stop signs when immediately going to accelerate again through it, passing and pick up speeds were greatly increased, and smoother!, and a much smoother idle (wasn't super erratic in idle before, but noticeable)

Any Ideas??? Is this telling me one or both of my o2 sensors are bad or sluggish? causing performance issues? I never had the supposed ECU upgrade/Flash after installing the new MAF sensor either...

Any thoughts on the matter?
Sincerely,
Love this car but going NUTS trying to figure this thing out!

[Kompresshun]

I've dealt with similar issues with my car, but not quite as bad. One thing I was told when I replaced my pre-cat, is that if you don't use an OEM Nissan one, it can cause problems. It's possible your Oxygen Sensors could be failing, but typically they throw a code just for the oxygen sensor.

Also, you mentioned you didn't get your ECU flashed after installing the MAF and I assume you didn't do it after the pre-cat either. I would think that this could possibly be your culprit here, as you're supposed to get them re-flashed after either of those things being done, in my experience.

I know how you feel though, i've been chasing down a noise in my car for over a year now and nobody can figure out where it's coming from. They're excellent cars, but things like this can make you lose your sanity with them!

[jsta22]

I feel ya on the noises as well. probably the noisiest suspension Ive ever heard on any car Ive owned! I know what the VQ is supposed to feel like, as Ive had a few friends in the past with Maximas, ranging from 97 up to 2001..and Myself have owned an 06 G35 coupe.. Gobs of power in each car!

To follow up, immediately after I wrote this first thread, I went out and re connected the o2's and went for a drive (about 15-20 miles) and right back to the weaker feeling start up, not the same acceleration as when the o2's were disconnected, and the early/not so smooth transmission shift is back again..

Makes me say i shoulda kept them disconnected.. Ugh!!!
You think I should get the ECU reflashed/reprogrammed? and do you have an idea what this SHOULD cost??

[loystock]

There is a possibility that the replacement part is defective/damaged. Did you or someone else dropped it during the process? The OEM Bosch sensor is expensive ($100+) so I usually go for the OEM-compatible NGK/NTK sensors ($60 more or less). You may also have to replace the pair of O2 sensor on the affected bank.