So, im new to this forum, and haven't had the time to look through all of the threads. With that said, I am a new drive, and I got my 99 Bonneville from my Uncle, with ~143k Miles on it. As ive been driving, which is not very much, I've noticed that I'm only getting about 12MPG... I cant believe this. Does anybody know what could be wrong with it? Other than that and a few other problems like a bad starter, a broken cupholder, and bad oil leaks, I love this car, and I hope that it is fixable so I can continue to drive it.

It should get much better than that, but there are several things that could cause this. Here are a few questions: Are you driving with your foot to the floor? Is the check engine light on? Has it been tuned recently? Is the air filter clean? Are the tires properly inflated?

Wow thanks for the fast reply. In response to your questions, Im known by my friends as one of the most cautious drivers- I dont ever let it go above around 3000rpm on a good day, meaning I really dotn accelerate fast. I have no lights right now, and The filter was just replaced. I do have tire issues which need to be addressed, but I do inflate them often, yet still get this poor mileage.

Take the time and money and polish her up. Fuel filter, plugs, etc.

its going to my mechanic tomorrow, and we'll see what he can do

Check tire pressure, should be around 30psi. If you don't know how old the plugs are, change them. If you don't know how old the plug wires are, change them. Check and clean the throttle body, check the PCV valve, replace the air filter if you can't see light threw it.

I asked my uncle what he had done with the car while he had it, and he said nothing other than tires and oil. So i have a feeling the plugs and wires are ancient.

Pull the plugs, I'll bet the ends are little more then a round nub. You should be getting a good 20+

Change the plugs, mine were burned out to just a little nub and it jas more better acceleration and power now!