1999 Century Acceleration Problems

My 1999 Buick Century has been experiencing sporadic acceleration problems. When first giving the car gas the acceleration chugs and the car has difficulty getting up to about 30 mph. Giving it more gas causes it to continue intermitten hesitation/sputtering. Only when I let off the gas and feather the gas in slowly can I get up to speed. Sometimes the problem is severe and at other times nonexistent.

The car has been to Buick dealer twice and an independent mechanic twice. They have cleaned the fuel injectors, changed the fuel filter, replaced the cadallidic converter, replaced two O 2 sensors, and replaced the throtle body. It seems that no one knows how to fix this problem... any suggestions would be appreciated!

Unplug you EGR valve and then drive it. If it drives better then you know where the problem is. I went through this last year. The car was in the shop over a month and returned unrepaired. Good Luck.