Hi, I have a 2001 infinity i30, 87,000 miles, recent tune up. prior to this service mpg was in the high 20’s now its in the high teens. oxygen sensors have been replaced, but this did not help. Any idea what to check next?

What was done on this ‘tune-up’? Have you checked the tire pressures? Have you changed what station you get gas from? How are you calculating the mileage? Is there a Check Engine light lit? If so, get the code(s) read and post them back here.