Idle speed too low

[Navistrpwr at aol.com]

About two weeks ago, I decided to finally fix the annoying exhaust manifold
tick on my 86 5kT.  I ended up pulling out the engine and sending the
cylinder head to the machine shop to have the 6 broken studs removed (about 3
were broke originally, I slaughtered the rest removing the manifold).  While
the motor was out I replaced all the gaskets associated with the cylinder
head, w/ the exception of the cam seal, replaced all 5
injectors/inserts/sealing rings, replaced the turbo oil and coolant lines,
and inspected the vacuum hoses going to the manifold etc.  I finally got the
motor back in and running a few days ago, but to my dismay I can't get it to
idle right.  The engine will stall out unless I keep my foot on the
accelerator.  I was expecting this to happen after replacing the
gaskets/repairing vacuum leaks.  I've adjusted the idle and CO in the past on
my non-turbo 5000 without any problems, but for some reason I do't have
enough travel on the idle screw to get the idle to the proper level (the best
I can do is about 400 rpm, at which point the screw comes out of the throttle
body).  I had a friend hold the throttle at around 700 rpm and measured the
duty cycle on the freq valve, which was down to around 25 %.  I turned the
adjustment screw on the fuel distributor and brought it up to around 50 %,
hoping that it would bring the idle up a bit as well (if this worked i was
going to go back and forth between the idle and CO, hoping to eventually find
a happy medium).  Unfortunately my theory was incorrect.  I'm at a loss for
ideas.  To my knowledge the ISV is working OK (i disconnected it, turned the
ignition on, and was able to blow air through it), and I replaced the
michelin man hose about a year ago.  The other turbo hoses seem to be alright
as well. Any help would be greatly appreciated.
                            TIA,
                                    Ray