(3.5 engine ) My rocker arm dowels broke and I replaced the dowels and while I was there I changed the spark plugs. I replaced the NKG plugs with the exact same NGK plugs . I put it all back togather and lost 2 mpg. I have checked the millage many times and got 26 mpg , now after the change I only get 24 MPG. Is there something I could have left unhook or got out of adjustment while replacing the dowels or plugs that could have caused this loss of MPG ? I have no check engine light?

 

Might try resetting the PCM and let it relearn the adaptive memory.