96 blazer runs rough, some times
 

Bought this 96 blazer runs great most of the time. Periodicly starts to run rough then smooth then rough again. No code in the computer, but as it smooths out ses, brake and abs lights come on then go off.
Have replaced distributor, cap and rotor, fuel spider. Tried wiggling wires on maf and computer with no result.
any ideas out there?