Help, High idle problem TBI, how the heck do you get it down.

[57NAPCO]

I have a 1988 Chevrolet V30, 7.4, 400 transmission. I have a high idle problem. On startup it’s idles way to high and never really drops down. Truck has low original miles on it. Changed...iac, tps, rebuilt TBI and new base gasket, pulled the egr and it’s not froze up, new fuel pump. Never touched the timing, could timing cause it on a TBI ? Sorry for the stupid question but I’m not a technician, just a parts changer...