vinicio75

I have a 2011 E350 sedan with 105K miles. I did a service B on it and replaced the spark plugs. I used Bosch YR7MPP33 plugs which are OEM for my car. I noticed that the mpg went down instead of up as expected. I was averaging 21.5 mpg with old plugs and now am getting 15.5 mpg. Only have been running with new plugs for a day. Is this normal? What could cause this problem? The car drives very good, It actually feel a bit smoother and picks up faster. I torqued the plugs to 16 ft-lbs..