take your car to a garage and have them dis-connect the "lock-up" I own a Olds 98 and I have owned 2 others. my other two had this issue. The lock up was the cause. You are also more than likely due for a tune up. I really enjoy my olds and I notice in the city it is a bit harsh on fuel but on the highway I get great milage (33MPG). Hope this helps, best of luck.

Agreed.  You could also have them replace the Torque Convertor Lockup Solenoid (or TCC solenoid) which is what Casper is talking about, as it only costs around $40 for the part and about 2 hours labor, and will increase your fuel mileage.