woke up to a problem, help please

my son drives my 95 sonoma, 4.3vortec, came in from work it was running fine last night, (i heard him pull in, it sounded normal) this am when cranked it runs like a old john derre tractor bad missing sound will only semi run under throttle , any ideals:banghead:

bump. please all input appreciated

could be the cpi unit if it has one, you didnt give alot of info
the regulator on the cpi units can leak along with the nut assy.

well i did not know what a cpi was. so i went back to basics, it was firing and had good spray from the throttle body injectors, new distributor cap and rotor button, did not solve the problem, however new plugs did, this is the first time i have ever had this type and severe a problem from plugs, usually it has been my experience that plugs will not go bad over night, however these where running fine when he came home and the next morning it sounded like it was running on 2 cylinders and then only under throttle, however i installed six new plugs and it cranked and ran perfectly, so i shut it off and also replaced the plug wires so now everything is running as good as when new.:grinno: :smokin:

If something(peice of carbon?) stops the EGR from operating normally it will cause similar problems. This could have eaisly gone away just as mysterouisly.

EGR valve needs to removed, cleaned and replaced with anew EGR gasket.

It is under where the intake attaches to the engine.