I disconnected the battery, installed the new MAFS. Now I’m getting slightly worse gas mileage. Is it because the computer is learning? I have only driven in city since I changed it not much highway.

 

Have same mileage dropping problem, it showed check engine than have clear all the codes (fuel injector, replaceed all the oxygen sensor by new one than by changing the catalytic converter). Now there is no check engine light but after few days later mileage is dropping same problem. Please help me to solve this issue.