u/SwiperBackedUp

I’m trying everything but I’m in awee I can’t find out what’s causing my horrible mpg . Probably about 26 city 30 -33 max highway I have a 2019 mirage le 135 miles. I’ve done many fuel treatments in the past 4 days please don’t suggest that. That code has been active for a while and my mpg on my dash is showing anywhere 26-33/34 avg. I do have code P0421 show up for bank 1 warm up cat but I ran cat cleaner and it disappeared and cars acting fine. Tomorrow I’ll be cleaning the throttle body and fixing that sensor. Anyone have suggestions? I was told do a smoke test for leaks in exhaust but that was for the cat code. And I really don’t think that’s it. I was told to replace the upstream o2 sensor because it could be lazy but I don’t got a code for it and I don’t got money to throw around playing guessing games anymore.

Originally when I got this car I’d average 33-38mpg or more. Now for months it’s been only getting 28-33 MAX mostly lower I did replace so much the main o2 sensor all sorts of suspension brakes rotors tie rods etc etc you name it. Well recently I got a p0421 code and my mpg is SOOOO BAD in a 2019 MIRAGE LE with 135k miles just hit… please help me I didn’t buy this car to get bad mpg I’m lucky to hit 23-29 max on city alone average it’s mostly around 28average city! I have ONE code which I cleared and used cataclean for my catalytic converter p0421 which is the heat up bank 1 below threshold … please help someone I want my good MPG BACK!!!! I’ve used fuel additives everything no luck ?! I’m calling all professionals in this fuel trim situation of what’s happening and why my mpg is so low. I don’t have any leaks I think either!

2019 MIRAGE LE

Originally when I got this car I’d average 33-38mpg or more. Now for months it’s been only getting 28-33 MAX mostly lower I did replace so much the main o2 sensor all sorts of suspension brakes rotors tie rods etc etc you name it. Well recently I got a p0421 code and my mpg is SOOOO BAD in a 2019 MIRAGE LE with 135k miles just hit… please help me I didn’t buy this car to get bad mpg I’m lucky to hit 23-29 max on city alone average it’s mostly around 28average city! I have ONE code which I cleared and used cataclean for my catalytic converter p0421 which is the heat up bank 1 below threshold … please help someone I want my good MPG BACK!!!! I’ve used fuel additives everything no luck ?! I’m calling all professionals in this fuel trim situation of what’s happening and why my mpg is so low. I don’t have any leaks I think either!

Every 5-10k miles or more my check engine light pops on for p0421 which says bank 1 catalyst below threshold. I just unplug battery and it stays off for a long time until maybe a month or few later decides to come back. Do I Need a new catalytic converter or should I just change the downstream 02 sensor?

My 2019 mirage le is great I’m at 135k miles do regular maintenance. I do have my tires not the best currently but far from bad. I noticed recently randomly upon hitting 60-70 mph my steering wheel and front end starts to shake pretty bad not horribly but not good and I can feel it in the whole car. What could this possibly be going on?