Iv got a 2002 blazer with 120,870 miles, the mystery is I'm getting engine codes p0171 and p0174. I have checked every thing that OBD-II Trouble Codes - DTC Codes Car Repair says for the issues. Found a Vacuum leak and a hose that was rotten. I have also had other codes but i was able to fix them. what i have replaced so far is the O2 sensors, spark plugs, MAF, and a new cat, the only code to fix is the p0171 and p0174. so i took it to a shop and had them try and find what was causing it and the only thing that they found was the fuel trim was at 24 and they said running lean is 25-26. But they said they don't know whats causing it. Anyone else had this issue or know a solution for it?