e 30 isc 90 caddy deville

I have the code e 30 on my 90 deville 4.5 v8. I replaced idle speed control motor with one from junkyard. I read i need to adjust plunger on idle speed control motor because my car will not idle unless i keep my foot on the gas and when i drive i have no power no matter how far i push the gas down. I followed the procedures to adjust the ISC but i can not get the plunger to retract by pushing with my thumb. Does this mean its bad? I read these Isc motors going out were a common problem on these old caddys did i get a bad one from the salvage yard? Should i be able to get it to retract by pushing it? I even tried pushing with a screw driver. How do i test it??? please help need my car back!