1993 Buick Century

Could be malfunction in transmission. If it's a four-speed, also check the vacuum modulator (round thing toward the radiator with vacuum line to throttle, make sure it holds vacuum, isn't leaking transmission fluid into the line. Also, if the transmission fluid isn't bright, cherry red, change it and the filter. Finally, if for any reason the throttle valve cable has been disturbed you might want to make sure it's correctly calibrated. It's on the throttle, with the adjuster mounted nearby. Depress the tab on the adjuster and pull it down from its bracket. Then depress the accelerator pedal all the way, and it should click into place.