Haha yes, certainly a pain to work on and I have the scars on my hands from the exhaust manifolds. I replaced with brand new Opti from ACDelco.
I’m using a very rudimentary scan tool (ELM327) doubt it has that capability. The wires were supposedly replaced during the last tuneup with the plugs 25k miles ago...the EGR was also replaced then and still looks shiny new.
I’ll check for vacuum leaks and verify vacuum reading with gauge. I think the O2 sensor voltages varies, but I will verify. Btw this car has 235k miles on it
Thanks for all your advice and insights!