Z-1000 will give full power to track even when “off” is selected on throttle

shouldn’t do that. If you bought new, return it. If you bought used.... try and return it. 

In depth here and here or here. Mentioned here, obliquely here.

there is probably nothing wrong with your z1000 it was not designed to run ps 1 engines those boards only work with certain transformers, I'd be willing to bet it will run old post war engines no problem! if you had a z4000 mth transformer your engines would take right off. the ps1 like pure sign wave but the z 1000 but you would not have  a pure sign wave output  ! an older zw would run those trains but you would not have the fast circuit breaker protection and would easily damage your electronics.

Alan 

Alan, reread his post, he get full power with throttle off.  That is a shorted Triac/FET or diode in the transformer controller.  Also, Z-1000 will run plenty of the PS-1 models fine. Yes, you might have some early 94-5 models that won't do well.  G

George is, of course, correct.  This is not that uncommon, it's actually a fairly easy fix to replace the triac (or two), seems some had one, some had two.