try checking this.
I also have a 16 valve that behaved similiarly. If you take a close look at the throttle body, there is a small grey switch attached to the throttle plate spring. I think the name of this is the throttle position switch. Remove the wire harness and the swtich with a 7mm wrench and closely inspect the rubber boot on the switch. I chaecked mine out and saw the boot was torn. I ordered a new switch, the part number should be on the switch, replaced it with the new switch and Voiola... Smooth idle.
It should run about 25 to 35 bucks and 15 minutes of your own time. I went thru all the mechanic BS checking the idle valve and replacing with 2 new idle valves, to no avail. Try checking it out and let me know what you find. Thanks, Joe