I have a 96 K1500 Suburban 5.7 with 175,500 miles. It has recently started misfiring at cruising speed. Not all the time, maybe every 1 in 6 drives. You can speed up and it will reset itself and run perfect until the next time it decides to do it. It gave me codes in this order P0340, P0420, P0430, and P1345. I'm no mechanic by any means. I can change the oil and do a basic tune up, then after that I'm done. Any help would be greatly appreciated.

 

Take it to an honest independent ASE certified mechanic. Codes can be warning of other malfunction, like an oxygen senderr code might not mean that a sender is bad, bit that it was having trouble with the air/fuel mixture instead. Most likely one malfunction gave you the 4 codes.

 

Thanks. With it being the weekend i will this week. Didn't know if it was something i could check myself.