Won't stay running, backfire, cherry red exhaust
 

I have a 2000 Mustang GT that won't stay running. It backfires and I can keep it running for a little bit if I hold the throttle down. When I do that the driver side exhaust pipe get cherry red. I've tested the fuel pressure, replaced the Idle control valve, cleaned other sensors. I had a code for O2 sensor come up prior to it stop running. My next step was to replace the O2 Sensors and check for the cats being clogged. what else could or should I check?

My money is on a clogged cat.

i had this on a different car but it turned out to be a cylinder misfiring and dumping its
excessive raw fuel into the exhaust

Clogged cats.

My buddy had this happen to his car, and it was a clogged cat.

^ yup, cats...

Okay, finally got the exhaust off. Still doing the same thing, no change and will not run. I don't know what to try next.

I also replaced plugs and coils earlier this summer and was running great until I shut it off the last day it ran.

I don't think it will run without the O2's connected . Are you saying you tried to run it with the mid pipe removed?

It wont run too well with no o2 sensors.