will check my fsm. will solenoid make a sound when it engages?

Solenoid was the wrong term. I apologize. That's what I get from going by memory.

Look in the EC section of the FSM. On the bottom right of EC-10, you get a very vague description of the throttle opener. That is what prevents the throttle from slamming shut when you are off the gas quickly. Basically, it uses the engine vacuum to keep the butterflies open some to prevent an overly rich condition. 

When the 280Z came out, the system that car used is known as the BCDD or boost controlled deceleration device. 

in ec 1 list check valve, control valve and servo diaphragm. is one of these the throttle opener.  does not show solenoid 

From what @SteveJ is describing it’s not an electric solenoid. It’s a vacuum actuated diaphragm .

ok, problem solved. faulty sparkplug. replaced all plugs. runs like a swiss watch. someone suggested this fix. kodos on him.