so ive got this 1991 sierra it ran perfectly when i got it, i let it sit for a month or so and now it wont idle. my father and i have been looking at it for a week now and changed and checked a few things that we thought could have been problem (checked the fuel pressure, changed the cap and rotor did some other stuff).
we then went to check the timing and unplugged the base timing wire and set the base timing @ 0*TDC, it ran perfect. when we went to plug the wire back in, it continued to not idle. anyone have any ideas on what the problem is?

it is a 5.7 motor and has 126k miles on it

did it run fine otherwise? check the iac valve. idle air control, inlet air control, some people call it the idle bypass valve, etc... it lets air in at idle (go figure)

when i first got it, it was perfect. if i try to drive it with the timing wire unplugged its rough, and i have to be constantly on the gas to keep it running.

unplug you egr valve and it will probaly run fine ihad the same problem with my 1990

the distributer was busted, i guess it rusted and just fell apart. (rusted cause my weather strip is bad). it runs fine now that i swapped the distributer, thanks for all your input on the subject. it helped me out a lot.