I have a 2004 mitsubishi Galant 2.4L. I have the check engine light with codes p0431 and p0421. Im not really sure what could be the problem if it's the exhaust manifold or just the o2 sensors. My car randomly idles a bit rough when im at a red light and it sometimes jerks when im on the highway going around 65 - 70 mph. I see the rpm go down quite a bit while idling. It rarely even shuts down on me when slowing down to a complete stop. I checked the freeze frame data on a obd2 scanner and got the following:
DTCFRZF P0172
FUELSYS1= CL
FUELSYS2= CL
LOAD-PCT (%) = 28.6
ETC (°C)= 83
SHRTFT1= 0.8
LONGFT1= 12.5
SHRTFT2= -0.8
LONGFT2= -12.5
MAP(kpa)= 37
RPM(/MIN)=726
vss(km/h)= 0
sparkadv= 16°
Lat(°c)= 18°
MAF(G/S)= 4.96
tp(%) =2.7

I just want to have some options before i have to replace the manifold. I have replaced the spark plugs, MAF sensor (helped quite a bit). Any help would be greatly appreciated!