I have a 97 chevy Suburban,LT 8 cylinder/gas/197k miles on it. Its been an awesome truck. Went for inspection & failed / Service engine light is on. Codes P0420 / P0430 / PO171/ P0174 / P0307 After I looked really close found a cracked vacumn line, cracked in half actually. Replaced it.. SES light went off. Could it really be that simple. for oxygen sensors and the MAF sensor codes ? I also had all kinds of work done plugs, plug wires, still getting the number 7 cyl misfire,, any chance the vacumn hose was causing that too.... The engine does stumble ever so slightly, its actually hard to notice but having the truck for a long time I can feel it. I also replaced fuel pump with ac delco pump about 3 months ago.. Any suggestions,, or what to focus in on will be appreciated.