Everything that you've done so far is a good idea. Not just to fix the idle, but in general. The replacement of the wiring harness makes for a good next step... cause really.. if your wiring is shot or you've got vacuum leaks you can't expect to set anything.

If you want to save a few clams, you can test the CIS coolant temp sensor (and probably the TTS as well) with an ohmmeter and a calibrated thermometer. Otherwise, replacing the two is a good idea.

The CIS computer is in the RH passenger's footwell, remove the plastic trim panel to expose the two computers (Lambda and CIS). The cruise computer is above the passenger's feet, the other two are to the right. The CIS computer has two electrical connectors on it, and I believe is the one on top.

Yes, you do want a more accurate tachometer than what's in the car. Something that hooks up under the car is probably okay (as long as you can read down to 10 RPM). Actually I was just thinking.. who has an exhaust gas analyzer and an accurate tach.. a smog shop. Go up to a shop that offers to do smog tests. Ask the guy if he'll help you set the fuel mixture (need to set the probe before the cat converter, engine/ignition off.. unplug o2 sensor, start car, fiddle with mixture until CO is at 1.0% +- 0.3%, engine off, plug in o2 sensor, CO should drop below 1.0%) and idle.

An automotive multimeter would be a fine way to go, and would usually include such things as an appropriate tach, dwell meter, DC voltage, and resistance. I would prefer an inductive tach (one you could clamp on to a spark plug wire), but those are a bit spendy.

P.S. That's a nut cracker.

- alex