My 93 Dodge Stealth ES is idling extremely low. When I do a cold start the engine idles and the tacometer reads a hair above the 0. When i drop it in gear (in drive, or reverse) the tacometer drops to 0. The car runs fine and doesnt stall when its driven, but Im curious why this is and I am concerned that it will stall at some point in time. Before this occured I previously cranked up the idle screw and things were going well for a while. Then I started noticing the idle was gradually dropping again day by day. This morning is the lowest it has ever been. What is going on here? Unfortunately cranking up the idle screw isnt gonna solve this problem.

 

It could be an idle control motor problem. Replacements can be had for under $100. If that doesn't work, then you may have to replace the throttle body.