I am at the end of my knowledge and need some help. I bought a 2000 TA with 224k miles on it to rebuild with my grandson. I probably should have bought a car in better shape with less miles but I like bringing things back from the dead. When I got the car the Cats we re clogged and after doing some research on here and pricing I decided to just do headers and high flow cats instead of replacing the stock cats. I also decided to do the motor mounts while I was at it. Beyond the headers and cats the car is stock. I did have to use extensions for the front O2 sensors (replaced while I was there) and I used bypass resistors from Summit and removed the rear o2s. I live in NC so I have to have emissions testing.

While doing the exhaust I took to a local shop to do the Y pipe because it was a few inches too long. When I got the car back it was throwing multiple codes from the O2s. I finally put it in the air and found that the shop had taken the O2 extensions loose and not hooked them back up.

After that I cleared the codes and took it out. Under WOT I would get popping like backfire from the exhaust, but no codes. After driving it for a while I got a code for misfire on bank 1 cylinder one. Thought it might be a coil so switched cylinder one with cylinder two. I also found that there was a sensor on the driver side at the back of the engine under the check valve that was not connected. After connecting the sensor it resolved the misfire code but the popping is still there and now I am getting too lean codes on both banks and an Idle Speed higher than expected. Here is what I have done:

Replaced entire PCV lines and valve when doing initial maintenance
Replaced plugs and wires
New check valves
Cleaned MAF with correct cleaner
Swapped MAF with known good MAF
Cleaned Idle Air Control valve
Checked all vacuum hoses for leaks
Sprayed cleaner around intake and vacuum lines to look for leaks
Seafoam treatment
Tested fuel pressure at front of rail (55-60 PSI at idle)
Changed fuel filter
Checked all exhaust connections and tightened everything under the car

I have a Scanner utility on my phone and it shows the O2s are active but drop low (0-0.1V) on acceleration. MAF is reading 4-5 g/s at idle. Idle is running rough around 860 RPMs.

I posted in the Gen III External forum and didn't get any responses.

Completely at a loss and not sure the local techs are going to be any better, please HELP!!!!

 

Sub'd. I am getting lean codes under almost identical conditions (except not running rough)

 

O2 sensors hooked up backwards?
Exh leaks?
Sensors fried by driving unhooked? Clogged cats could have fried the sensors, too. [overheated]
Lean codes could also have been set by the headers leaning the engine out. Might be a good time for a tune.

 

O2 sensors were replaced with the headers and seem to be working. Fixed and tightened all exhaust leaks. I am leaning (pun intended) towards just needing a tune and have one scheduled but they can't get to it until January. Really don't want to wait 2 months to go for the tune to find out there is another issue.

 

I'd say to check the voltage and Fuel pressure at WOT, if possible but idling high too high and popping are classic intake stream leak symptoms. I know you said you checked the intake but did you check anywhere between the MAF and the throttle blade? Maybe some unmetered air is getting in there? Just shooting in the dark.