I’m 18 years old, bought my 2000 eclipse GT at the start of ‘22 and have been trying to figure out what is wrong that’s throwing the P0420 code. I have a small budget so i’m trying to avoid replacing this and that in order to figure out whats bad.
The car has 183,000 miles but it’s been issue free since i got it (at 172k) aside from this. I always do an oil change after 3000 miles w/ OEM filter and mobil 1 oil but otherwise haven’t done a thing. It had a new cat installed just before I bought it. the first 8 months there was no codes at all, and then it started to pop up and go away, sometimes every few weeks at random. This makes me think the previous owner replaced the cat when it got damaged, but didn’t address the cause of the cat’s failure, and obviously i don’t want that to happen again.
I made a list of all the car’s symptoms, maybe someone can make sense of it?
-lags when accelerating(sometimes more than others)
-there is a hissing sound under the hood close to the firewall (vacuum leak??)
-gurgle sound when feathering the gas from a stop
-rattle/gurgle sound lasts 2-5 seconds, only after startup, sounds like it’s coming from the rear, and doesn’t always happen but usually worse in cold weather
-when steering wheel is turned nearly all the way, it makes the RPMs change and sounds way worse than other cars would
-when driving ~2500 rpm, seems to have trouble shifting gears up, like i need to gas it excessively, and the exhausts tone makes me cringe
-idle is sometimes rough, but sometimes flawless
-battery has died a couple times in the cold
-lifter tick that goes away when warmed up (usually)
-gas mileage fluctuates, but seems a bit lower than it should be
I know not all of those are relevant but figured i’d include it all for good measure. i know all the basics of what the engine code can mean, but maybe there’s someone out there with more knowledge that can help me discern the problem. or even if my engine is running rich or lean, i can’t tell, it seems like it has been both. any help i’d be grateful for!!!