Hey everyone, for the past 2 months I've been getting about 23.3 MPG instead of my normal 27-28 mpg. What can I do to troubleshoot this or should I just take it to the dealer? I've got about 2k left on the bumper to bumper.

 

i got exactley 30mpg today on a 300 mile motorway round trip sitting at 60mph with cruise on.
not bad at all imho..me deisel work citreon only manages 42mpg on the same journey..me bike about 35..me bike is like sitting on a rocket though lol

 

Things that affect fuel mileage and nowhere NEAR a complete list:

1. driving style
2. tire pressure
3. traffic
4. driving style
5. road conditions
6. weather conditions
7. driving style
8. % ethanol in the fuel
9. resetting the onboard properly
10. driving style
11. not USING the onboard and hand calculating
12. air filter
13. driving style
14. brakes dragging
15. dirty injectors
16. driving style
17. lead foot
18. # of traffic lights

And did I mention driving style?

 

If you take it to a dealer I'd be interested in learning if the Bama tune voids the warranty.
Other things that kill mileage: worn rings due to running rich-washes the oil off the cylinder walls and the rings wear down early. Valves not sealing 100%, can be caused by running lean and having the valves running hotter that stock. These are the three reasons I do not have a tune.
I did not see if you have an auto or manual-Autos can hurt them mileage if they are low on fluid, not shifting at the proper time, or if the bands are out of adjustment. Bald tires can lower your mileage-they don't roll as well as tires with tread. Poor alignment can lower mileage-you car rolls better when the tires all point the same way. Wheel bearings that are too tight will hurt mileage-you don't need to hunt for this one, the bearings will get noisy and fail. Running too cold will hurt the mileage, does the temp gauge read normal?