I don't know if it will work for all other Hondas but it worked for me like a charm.
A few weeks ago I serviced my whole car which was long overdue, Engine and transmission oil change, Filters, Valve adjustments, TB clean up, IACV, Plugs and Wires, Distributor cap etc, Pretty much everything.
(Car in question is a 88 civic with a swapped D15b "3 Stage Vtec")
But just as I was happy that the car was as good as new the Idle after the first few start ups went crazy it would stay up at 3 to 4K sometimes even jumping to 5K then at times it would just come down and stall altogether.
Safe to say I wasn't happy after spending so much and then getting these results but I did some online research and resorted to Honda Manuals which clearly states to Reset the ECU after such a major tune up specially when the TB is taken off and cleaned up also I came to know that a Vacuum leak in the intake system no matter how small would have noticeable impact on idle position and overall performance.
The procedure to reset the ECU in the manual was neatly laid out but was a bit too much precise for my lazy mood so what I did was take out the battery for the night and put it back in the morning, The car also had a vacuum leak in between the TB and the intake manifold where a small pipe connecting the two was missing, got that fixed started the car up and noticed it idled quite normal than before but it wasn't 100 Percent, So as stated in the manual took it out and drove for about 4 to 5 Km and everything was back to normal the car idled between 7 to 800 rpm on operating temperature and bit higher when load is put on, The cold startups in the morning have also improved alot.
So if you haven't done this already give it a try it worked for me and it seems like you have pretty much the same problem and since your problem is related to AC do check carefully for vacuum leaks which most likely seems the case. Also do remember that you need to run the car on petrol to reset the ECU and drive it so it can relearn the settings and once everything is done you can switch back to CNG.
Apologies for all the long info but it seemed like the alot of people have these idle issues and sometimes there is a simple and inexpensive solution that people aren't aware of.
