This thing is kicking my butt

[no_rice]

Normally I'm over in the 67-72 with my 70 GMC Shortbox, but..., I picked up an 89 GMC 5.7 auto, thats been sitting in a garage for the last few years. And getting it running right is giving me fits... it does have gibson headers, and custom exhaust on it, but other then that, motor appears to be reasonably stock.

for the most part its at a point where it fires right up, but it does not want to idle right, and its super rich. the idle air control was not functioning correctly, so it was sucking a ton of air all the time and couldnt slow it down. so got a new one of those. but even after doing an idle reset on it, the iac still does not completely close, even when the truck is good and warm. so it still idles a little high. if i slow the idle down, it will stay that way for a minute or 2, then die down to a stumble and start puffing smoke and running rich. give it a little throttle or speed the idle back up a hair and it cleans out and stays that way, but still idling a bit higher then it should (no tach, so going by ear, but obviously a reasonably fast idle speed) and sucking a little extra air through the iac (atleast i assume at operating temp, in park at idle that thing should be closed off)

when getting it to run, ive already replaced cap, rotor, plugs, and new wires. checked fuel pressure and its good, and some fresh fuel. as well as what appears to be a good cone shaped pattern out of the injectors. checked for vacuum leaks and have found none.

looks like im going to have to replace the harmonic balancer before i can get a good timing check done, because its wiggling all over the place while running. so i assume the rubber inside is shot. but as good as it starts and idles with even a little throttle, i dont see that being to far off. that being said. even when its idling at a good pace and fairly smoothly, a quick whack of the throttle can make it backfire through the throttlebody