Do not for the love of God remove the o2 sensor and run it like that. I stupidly did this at the behest of a friend whilst disregarding my own better judgement and severely damaged the firewall insulation in a matter of 10 seconds.

Any recommendations of what to check? I was thinking maybe to pull the O2 sensor at the cat or front ( which one?) to see if it could be a plugged CAT. I haven't replaced that in a very long time... Is that a wise move? It has the symptoms of a clogged exhaust system. It could be any component in t...

That’s a plugged cat , for sure. You can put a pressure gauge on the OXS bung and measure the back pressure for fun.