Help with idle misfire on Nissan SR20DE (Primera P10)

[aldi]

This is starting to drive me up the wall a little bit, can anyone suggest anythine else I should check? The car starts normally from hot or cold, and doesn't stall. Fast idle is fine untill the car warms up and the idle drops. It cruises fine, and gets book economy over several tanks. Power 'feels' a little bit down over the mid range but really takes off over 5K. I haven't got the cash to just throw random new bits at the thing at the moment. Here's what I've done/checked so far -

TPS adjustment - was a little bit out, now spot on. Much smoother on/off throttle now.
Dizzy cap/rotor - no esessive wear, rotor resistance within spec, no sign of tracking.
Plugs + HT leads replaced, no effect.
Coil + ignitor check within spec. Cleaned externally + all contacts, no effect.
Cleaned all the various grounds around the engine bay.
Ran with TPS disconnected - misfire still there.
Base idle + ignition timing checked OK
Checked for vacumn leaks by poking an unlit blowtorch around the engine bay
O2 sensor - It's a 3 wire type, I can see 12v getting to the heater, but between signal and ground I can only see a steady 120mV - it should cycle between <200 and >700 right? But then again, the display updates quite slowly on my meter so I don't know if that's a true reading. You can put the ECU in a mode where it flashes the dash light according to the O2 sensor rich/lean and that seems OK
I'm getting an intermittant code 34 for the knock sensor, which I guess might be why it feels down in the midrange, but that wouldn't cause this problem would it?
I'm going to borrow a 'scope this week to check the CAS output from the dizzy.

Is there anything I've missed? Can the collective brains of the PH massive help me out here?

Neil

[GreenV8S]

From the title I guess the problem is an idle misfire, but you haven't said anything about it. Are you dropping a cylinder at idle, or is it just a bit lumpy (cylinder-to-cylinder variation), or what?

[aldi]

It's very lumpy, and it doesnt seem to be the same cylinder each time. It just sounds very random and lumpy. It can run fine for 2-3 seconds then *phut* *phut* then fine then *phut* then fine... etc.

[deltafox]

O2 sensor should fluctuate between 0 to 1.0 volt continuously.

If its a steady 120 mv then its stuck....knackered.
Dosent explain your random misfire explanation tho....check plugs, leads, dizzy etc (if its got em).

[v8guinness]

When the idle control valve is giving up the idle will alternate between a fast idle and a slow idle every second or so, unfortunutely they are not cheap for these cars...

[aldi]

Cheers for that, I'l have a poke around it and see if I can clean it out at all.

Last thing I did was get rid of the knock sensor code by virtue of a 1 megohm resistor no effect