Henry - check the piston in the idle valve and make sure it is not sticking - if it is sticking it can cause the problem. Look into the bore of the valve with a bright light and see if there is any crud residual in the bore that could be causing the valve to hang up. Don't think you have a major problem here. Don't forget the sensors on this car cause different things to happen when engine is in park, drive, ac on - off etc - if the motion of the valve required by sensors does not happen idle will be affected. To see what I mean - pull the electrical connector off the idle valve and watch the revs pick up. OR - just drive the car for a few days and see if the valve frees itself up - if it worked once - it should again. In fact - after you put the filter in - I'd just drive the car for a few days and let the dust settle - then look at the idle at that time - easier and won't hurt anything!
This head mod you mention - the seal is good all the way around the valve cover except at the outer rear corner of the valve cover - the oil leak is very small - just a drop or two in a minute - but enough to cause smoke and smell - when I turn left the oil is pushed up against the outer part of the valve cover and the rear corner starts it's little drip - Do you think this mod around the injectors will cause the leak at the outer rear??