69 chevelle 350 rebuilt the motor
slight cam (1 step above stock)?
double timing chain.
stock rebuilt heads,crank turned.,

cruise idle is a problem.

if I go 35mph and let it at (cruise idle) at 35mph
I get poor idle stability. :(
even at any cruise mph 35, 40 25, 30

the engine runs ruff(poor idle stability)

I think there is no vacuum leaks (intake).

carb.? distributor? or the dreaded
gas tank cap? (vapor lock)???

car runs great when acceleration,slowing down
or at stop idle.I can punch it
and the engine response is GREAT
at stop idle. I can run the carb.
accelerate. and the engine response is GREAT

what is my boggle?

can anybody help me ?

I am missing too many cruise nights.
thanks
AL

Have you checked the carb float level?

sounds like a lean condition, you might have a small particle covering one jet, the enrichment circuit partially makes up for the lean condition when you put the hammer down, the idle circuit sounds like it is alright if it idles fine and stays running when you brake. It also might need to go up a couple of jet sizes. What carb is on the car? Your gas cap should be vented I would think, loosen it up and go for a ride-I bet the problem remains.

I can rule out the gas cap idea. The 69 gas tanks have a vent on them at the one corner with a little filter on it so it doesn't matter which gas cap you have on there.

rochester quadrajet 4 bbl

I have 2, I keep swapping both of them on the car
1 is manual choke, the other is electric.
the engine rides the same with either , or.
maybe I need a new carb.??

Yup, not a gas tank problem. You have issues with the carb. Sounds like one side of the priaries is not feeding; probably junk in the main passage on that side.