OK I know a little about cars. So far sportages have produced the most problems. This thing STILL missfires. Brand new plugs wires coils coil boots I've dbl checked for arching..none. MAF and IAC cleaned and operating. Vacuum is tight and secure I've checked and replaced hoses. New PVC valve and gromet. Fuel filter new in last year. No problems with battle or alt. Main problem is random missfire at idle and at higher rpm? Maybe an o2 sensor and if it was would it be the upper or lower? Advice on how to check them with a volt meter.. ect? I love advice!