Love my 92 Park Ave (not ultra). Purchased used last year. Had read on other forums that some people got as much as 30 MPG. I got 20 whether I was in town or on the highway. O2 sensor replaced, no difference...so I decided to live with it. Now suddenly I am getting 15 Mpg? Anyone have any ideas. Hate to go to Buick dealer because they want $300 to look you in the eye. Appreciate any help. Thanks! J

I had the same problem. It turned out that one of the Vacuum hoses came lose. The MPG went from around 14 to 26.

Thanks so much. I'll have my mechanic check it out and let you know if this was the problem. Appreciate your help! J

I'd check the coolant sensor on the vehicle. It may be going bad on you.

That's interesting, my coolant low light has been going off for a month or so (even though thecoolant is low) I just ignored it (except to check to make sure the coolant wasn't low occasionally). I am still waiting to have my mechanic check the vacuum hoses, but he did say that he thought I would have noticed a significant loss in power if that was an issue.

Again, I'm curious as to what the connection between mpg and the coolant sensor is. THanks so very much!

I'm talking about the coolant sensor for the computor. It tells the computor the temperature of the engine and accordingly the idle control valve is controlled. The colder the sensor (temperature) the higher the idle and the higher the temperature, the lower the idle.
If you have a bad sensor, the idle will be considerably high (may not be noticable unless you have a gauge).
Also if the vehicle coolant temperature tends to be on the low side, it will give the coolant sensor a low reading causing high gas consumption.
Good Luck.

I never noticed the loss in power with the vacuum hose disconnected. The only thing that I noticed besides bad MPG was a rough idle. When I reconnected the hose the gas mileage increased and the rough idle went away. Hope you get the problem solved soon.