Help! Tbi Idling problem!

[espcamaro]

Hello everyone, this is my first time using this forum and it seems like it could be very helpful. I have a 1987 chevy silverado with a 350 tbi. It has a weird idle to it, it idles up and down. I've changed the iac, and map sensors. I've also changed plugs and wires, cap and rotor. I don't want to keep pouring money into on parts it doesn't need. I've checked the timing and it's dead on. Also, when I'm driving it, it tends to bog down for a second at full throttle and sometimes backfires. I have a tbi spacer so could that be some of the problem? I think that everything? Any ideas would be greatly appreciated!
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