88 gxl, 900 miles on new engine......

driving fine, good power, plenty of oil & gas.......turn it off after driving about 15 mins, cut it back on after sitting 10 mins, motor starts shaking, hesistating, doesnt idle fully, if you give it gas, goes on fine, voltage was bouncing between 12-14 volts back and forth....check engine light DOES NOT come on. help?

 

Will it idle alright if you open the throttle slightly? There is a mechanism that holds the throttle open slightly when the engine is just starting up and closes when the engine is warm. When you shut down the engine this mechanism may not reset in the time frame you mention.

 

Check the condition of your grounds:
With the engine idleing the headlights on, measure the voltage drop from the alternator frame to the battery negative post.
It should be almost zero.

 

Hot-start heat soak is a problem on EFI rotaries, which is why Mazda uses the Hot-Start Assist System to increase fue pressure and idle speed after hot starts.

Check to see it's working properly. It's covered on page 4A-80 in the S4 FSM. If you have it, there's better info in the S5 FSM on page F1-58.