Hello, longtime reader but have finally reached my limit on what I can solve without asking the question.

2006 GT, automatic trans, pretty much stock, 141k miles. woefully under used since March 2020.

I recently noticed i had a stuck P0430 code:Catalyst system efficiency below threshold (Bank 2) message. A week ago I noticed that the car sometimes wanted to die when you gave it gas, or if you were coasting then tried to accelerate. once I powered through it, the other time I coasted to a stop and restarted.

Drove the car over the weekend and woke up yesterday to a dead battery. Not the standard dead battery where nothing works, had a little bit of juice for dome lights and the window to drop open. Also had some clicking in the dash that i don't usually hear. battery tested at autozone as dead, replaced it and turned on the car to relearn the idle. After the engine got to temp I turned on the AC and the car immediately started surging in RPM then sounding like it was going to die. Also the message center would alternate with "Check charging system" and "Check gas cap" with each RPM surge. Turned off the AC, drove it around the block slowly and it died half way back, P0430 code gone and no other codes. Put it to bed for the night.

This morning I cleaned the MAF and the throttle body and started the idle relearn again, same results. I did a walk around and looked under to see if anything was amiss, and it starts leaking coolant from under the cap.

I came back a bit later after everything had cooled off, put the key on and ran through my data stream. Fuel pressure was 31 psi instead of 39, so maybe not the fuel pump giving too lean gas and overheating? I'm going to go drain the radiator and at least fill it again but i am not sure what to check next.

I can't figure out how all this goes together, unless i have a bad alternator, and a vacuum issue, and a fuel pump or filter issue?

 

Or a clogged catalytic converter on bank 2 (driver's side).

 

I agree with a possible clogged cat. If you check your fuel trims. If P0430 is the only code, your fuel trims will be very odd on the side with the clog. (be very negative) compared to the other side.