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if its running fine on the highway and acts up only at idle, tham I would say while the car is at idle remove airclaener and with a flashlight in hand look down inside the tbi and see what the spray...

what does the engine do when you step on the gas?

and does it try to surge when driving?
unable to maintain a steady speed on highway?

if your sure there are no vacuume leaks, then I would suggest that you either call around to see what shops near you have diagnostice equipment, to test sensors and look for trouble codes.
or you...

have you checked the ECM for trouble codes?

sound like you are having multi problems with the engine.
my wife has a 86 firebird transam, the original 305 in it bit the dust 4 years ago,

I had...