why low MPG
That is a major drop in mileage. I would start with a tune up and filter change. Have the catalytic converter inspected and make sure they check the plugs for carbon fouling in case you have a leaking fuel injector.
Is the vehicle running poorly? Check engine light on? Any new noises?
Search Pontiac Bonneville Questions
Pontiac Bonneville Experts
Related Models For Sale
Used Cars For Sale