1990 Mercury Sable Car Problems Help

I have a 1990 Mercury Sable GS
when i dont fully stop like at a yield sign and it goes under 15 mph, when i mash the gas it will rev up to about 4,000 rpms and then jerk real hard, i was wondering if anyone might know what it is thats causing this. its a auto transmission.

Well, we'll see if this gets viewed since the original message is over 2 years old. My BMW had a similiar problem. If you had the transmission fluid changed you may need to have the "check balls" replaced. No, I'm not making this up. They are about the size of a bb and they are in the transmissions throttle valve. Most car makers started using plastic check balls since they float better in the fluid but they tend to wear down ever so slightly with age. Eventually, they get stuck in the valve and you need higher rpms to make them pop out. Of course your car will lurch forward and then you can go to higher gears. See my other post under the BMW forum for more details.