1994 Buick Century • 105 miles

Intermittently, the engine runs with an advance-and-retreat motion, system is burning rich. I can smell the exhaust. At one point, I could not back out of a driveway. The engine would start, choke and gasp, then die. I had it towed to a mechanic and he ran the throttle by a lever under the hood and it cleared. What is this likely to be? I have had a tune up and an oil change last week which keeps the problem under control a little better. It still occurs.
December 14, 2012.

You need to check for trouble codes. Most parts stores will do it for free. It could be so many things that are causing it to run that way. If there are trouble codes stored in the computer, you will know where to start.