1982 Camaro Berlinetta 305 cui electronic Rochester. 4000 miles, yes 4000.
Problem is engine vibration. Strongest at 1500 rpm and 2300. Replaced converter, harmonic balancer, engine mounts, transmission mount. Disconnected all belts, plugged all vacuum, spark plugs, rotor, distributor cap, sp plug cables, firing order checked. No improvement. Also with slow acceleration, hesitating at 1200 rpm and sudden drop up to 400 rpm. Vibration is the same parked or driving. Beforehand thank you
PS. Flex plate also replaced.

 

do a compression check-how does it idle ?

 

Thank you for your tip, I absolutely agree.
Unfortunately winter came today and I will not drive on salty roads, so driving to my hobby garage for compression test might wait till spring. Weather forecast says 2 days with rain from tomorrow so maybe.
Idle is not bad, but not perfect. Smooth, but when watching the engine it is possible to see its shakes a little, cyclic like every 2 - 3 seconds or so. Can also feel it sitting inside. A "normal" person will say the idle is fine.
Fuel economy is not bad, on a long trip 20 mpg. This car was sitting from 1982 to 2012 with only 72 miles on it. Carburettor might play a role for the rpm drop, but not for the vibration I think.

 

balance test

disconnect each spark plug wire one at a time and note any that don't cause a change in idle.

 

Thank you, I'll try.