1994 Pontiac Sunbird slow idle

When the engine is idling, the car shakes just enough to make dash and muffler vibrate (very annoying). The idle is too low.
There is a screw on the throttle linkage that resembles an idle adjustment screw. Is that what this is for?
I took the idle control valve off and turned the ignition on and off and the pointed plunger moves in and out.
While its idling, if I barely touch the accelerator pedal. The idle will increase to a good speed and runs perfectly smooth.
please help.