A couple of probably obvious things. Its important to make sure the linkage is set so its not impeding your idle setting endeavors. Sometimes, the idle stop screw near air intake has been (incorrectly) used to adjust idle -- it essentially pushes on the linkage to add throttle. Make sure there is some space between this screw and the linkage stops.
Second, using the idle air mixture screw mentioned by Naj, you can use a vacuum gauge to establish the best idle speed to idle "sweetspot". With everything else (dwell, timing, plugs and linkage) all close, the idle should get you in the 750-900 range. Mine likes things a bit high -- when warm in gear is roughly 800. In park it raises to about 850-900.
Two helpful threads maybe my own travails here: (by the end we had it narrowed down to linkage -- and after my Dwell/Timing 101 lesson in another thread all has been very steady)
http://www.sl113.org/forums/index.php?topic=6859.15And also in the wiki, the ever-helpful "Basic Fuel Injection Linkage Adjustment and Idle Adjustment Procedures" under the fuel system link... everyone here should memorize this one...