idle/stalling problems until warmed up

[cad_90]

I just bought a 1990 Deville, and it starts fine, but will stall out once it is put into gear unless it is warmed up at least 5 minutes.

The guy I bought it from suggested that it was the choke that was at fault. I assume he meant the ISC (idle speed control motor), which is attached to the throttle body.

The idle seems slow to me, though I don't have a tachometer to check it.

Am I right in assuming that the ISC uses its plunger to control the throttle?

Anyone have any ideas? Don't want to just go out and buy the part if that's not it.