How do I adjust the idle speed? on 1993 Dodge Intrepid

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Engine idles fine in park, but when put in drive, idles very rough until engine up to speed.
(1) Answer
(2) Comments
does it run rough when revved in neutral?
No, once you rev it, seems to smooth out. Idle smooth in park, but once I shift into drive, idle is very rough and "bounces" or "shakes" the car until you start driving. When I slow down or stop while driving, like for stop sign, traffic light, etc., idle is rough again. The car sat untouched for a year before I bought it and was very dirty. One site I went to said the IAC could be dirty or bad, but I have no idea where it is on the engine or how to clean it.
very possible that site may be on to some thing. you said the ride sat for a long time. there could be an issue of old fuel and residues in the fuel system. you can help this by adding an ethanol treatment to your fuel. this will clean residues that may be inhibiting your fuel delivery. also add fuel stabilizer to help remove any moisture in tank. moisture can cause rough idle.
you may want to get ride tuned up if you haven't already. get a diagnostic run on it to see if anything else you need to be aware of. tune up you can do yourself. diagnostic free if you know where to look.