Idle control valve question

[kwken]

Hi Guy's, I have a question about an idle control valve. I had a problem with my 1991 420sel. I have done a lot of work on the fuel intake system. Most of my problem turned out to be old gunk in the throttle body and a new set of plugs. Now the only thing remaining is a little problem with the idle in park. It idles at about 1000 rpm's in park when warmed up. The vacuum gauge is a little to the right of 0. When I put it in drive it drops right down to 600 and the economy gauge goes right to zero. I have tested and cleaned the valve and it seems to be good. I noticed that if I put 12 volts to it I could still blow through it a little bit. My question is should it be a solid shutoff? If it did not shut off could it be a little vacuum leak? Thank you for any thoughts you might have. Ken