'86 5kT idle problem

[JordanVw@aol.com]

today i started up my '86 5kT, and it idled very low - more than usual, 
(usually idles around 9k rpm)  when i reved the engine up, and let my foot 
off the accel, it nearly died out.  i tried adjusting the idle adjustment 
screw in the intake manifold, but that didnt help.  after i drove it for a 
bit, and it was warmed up, the idle came up, but still not to where it should 
be.  any ideas as to what's causing this?  
it wasnt any colder last night than the night before, and this is the first 
time ive noticed this. 

TIA-
chris
'86 5kT, TQ