90 Buick Century Stuttering

HI
I have a 90 Buick Century with a 4 cyl. engine. Lately It has began to run rough. It stalls sometimes when Idleing and pulses when it is ideling. Also when driving around 35 to 50 mph it begans to stutter when I let off the gas. When I accelarate it runs smooth just stutters as if it is cutting out. I have replaced the plugs and wires, fuel injector, fuel filter, and have no check engine lights on. Any help on ideas would be greatly appreciated
Thank You
:banghead:

My 87 had same problem, felt like car shudders when driiving freeway. Was diagnosed as crank position sensor. It sits above the timining pulley outside of block(sorry, I know car has no timiing marks and my parts definition is none too good). When engine was under load going up hill or bottoming a hill where load changed, engine bumped. It didn't cut out, but was really disturbing. My engine was a 3.8 V6.

All the other parts you changed were ruled out before this part was changed.
I also changed a mass air flow sensor under warranty in first year, that would make engine die when accelarating onto freeway.

I never had any warnings or lights..

Thanks for your response. I will try changing the crank position sensor and see if it works. I appreciate your help:)