If you've got an LX, it's most likely a vac leak. Check the small stuff for vac leaks first.
Does it surge up and down in park or N?
Does it smooth out in gear?
Does it kinda half die at stoplights ocasionally?
Chances are it's the intake manifold gasket at the head. That's what finally fixed my surging problem. A few other members on ERDT have had the same problem, cured by a new intake manifold gasket as well.
Of course make sure you have your bases covered and check the simple stuff before you undergo the intake manifold gasket. Ie, good airfilter, pcv ok, fuel filter not clogged (put a new one on), plugs, IAC is ok, etc. You may also want to check your fuel pressure as well. If it's too low, in-consistant, or the pressure regulator has gone bad, an erratic idle will occur. Re-set the ECU as well.
It's a fair bit of work to change the intake manifold gasket and do it right to avoid problems later on. :wink:
Sirigan: Idle speed is non adjustable on 1.9's, nor is ignition timing in any way.
Matt 8)