idles funny sounds like a harley

ok the other day i was going to help a friend broke down i get there shut the truck off we get ready to leave i start it back up and it sounded like it was missing real bad sounds like a harley if i start it up if changed the plugs wires cap rotor but nothing has worked it smokes white smoke real bad and still sounds like its missing it starts up fine reves up fine sounds like it boggs down when i try and rev it up its a 1990 b2600i fuel injected 2,6 i was thinking the computer might be messed up but any suggestions would be greatly appreciated thanks yall

Earl has an excellent post of what your capacitors on your computer can look like.

The white smoke is a worry.
White usually = coolant.
Coolant usually = head/gasket.
Pull plugs and see what colour they look to be.

i pulled the plugs and a couple are black and yes the smoke smeels like coolant a lil bit and if the head gasket blows would that make it run funny thanks for the info

yea if your head gasket went and your burnin water/coolant, it probly will run like ass. and that would be shity to go help somone and then ur ride fucks up. lol

yep lol hes thinking he did something but i just bought a head gasket and valve cover gasket im gonna change them out tomorrow and hope for the best thanks