Mixture above 2000rpm is controlled by the EHA, and looks like you have no problems in that area. sounds like you have problems with idle control and quite possibly idle mixture.
You might like to monitor power to the ICV at idle to see if you can get any insight there. Set a multimeter to measure 10v and touch the pointers to the ICV connector pins. You may need to slide the connector off slightly to allow some clearance.
If the circuit is correct, you should see around 6v across the contacts at KOEO and while the engine is idling. Based on my own experience, i expect you to see the voltage drop off and come back on again, matching the idle fluctuations.
If that's the case, you either have a defective OVP, a bad circuit somewhere between the ECU and OVP or the OVP and the ICV, or your ECU is bad, like mine was. (love those TLAs!)
This all sounds awfully familiar to me. I've just gone into the idle mixture issues at some length in a recent post. i've been wrestling with this problem nigh on two years now and only just found out it was the ECU that was at fault.
http://www.peachparts.com/shopforum/showthread.php?t=132197
Could of course be something else entirely but check the power to the ICV first. My money's on that.