Drivability specialists..I need help!

[rfmaster]

Back firing through TB indicates that ignition timing is off or you have a valve opening at a wrong time. On high millage engines OE timing chain is known to stretch causing valve timing to be inconsistent. During 70's and early 80's GM used to install plastic cam/crank gears in a stupid attempt keep engine noise down. I have seen timing chain jump a tooth or two resulting in wrong camshaft timing vs. piston travel! Since you have replaced every sensor on your TB it looks like it might be engine mechanical and not EFI related issue.

Check your harmonic balancer outer diameter ring - high millage balancers are known to slip exterior ring (due to deteriorating rubber) resulting in incorrect ignition timing indication.

Run a compression (or better cylinder leak down test) check - if there is a stuck (or burnt) valve that will catch that easily before doing anything else.

//RF