Misfire, evap, cat efficiency codes … I’m a little lost

Looking for a little help. I’ve been throwing 0420 and 0441 codes for a while, now a slight misfire just started. Current codes are 0171 system too lean bank 1
0420 cat system efficiency bank 1
0441 evap system incorrect purge flow
0450 evap system pressure switch
And I’ve got a pending 0300 random misfire.

Im too busy right now to work on it so I’m taking it in to a shop, we’ll see how that goes. What I’m hoping is I can get some advice on which of these are concerns -

I’m sure they’re going to try and sell me a new cat but I *think* on the first gen it’s only the first O2 sensor before that cat that talk to the eve to control fuel/air mix and a burnt up cat doesn’t effect anything other than emissions. Is that right?

What about the evap issues? Is that also just an emissions thing or is that going to be causing my rough running issues?

just not sure what I need to be fixing and what I can kick down the line a bit.

 

They are ALL important and they are all related. I am suspecting that there is a split vacuum line in the purge system or a stuck open purge valve. This will cause a lean condition… enough for a misfire, maybe. There might be more than one thing going on here. I would fix the evap before replacing the cat. There is a relationship between the front 02 sensor and the rear 02 sensor with how fast or slow the rear 02 sensor responds to how fast the front 02 sensor “switches”. The front 02 sensor voltage changes very fast and when graphed it looks like the teeth on a wood saw but with extremes in the height and length. The rear 02 sensor should have a long slow ripple wave pattern. If it mimics the front 02 sensor then the cat isnt doing its job. The system is not perfect, vacuum leaks in the intake or exhaust leaks can “fool” it and trigger a P0420. If it were me I would fix the evap stuff and see if that effects the P0300 and drive her.

 

thanks this is really helpful. I’ll start with the evap then. The cat is original, so 24 years old now, seems like it would need to be replaced? It’s been throwing that cat code for a long time I was just under the impression that it was only an emissions alert and didn’t have anything to do with driveability