3SGE idle issues

[GDII]

Cars is a 1990 SW20 with a GEN2 3SGE. I've been having idle issues for a while now.

Here's a bit of background on the car. I'd been having similar issues a long time ago with low cold idle but normal hot idle. This was due to the IACV being gummed up with oil and dirt. I dissembled the valve and cleaned it out, reinstalled and the idle ran fine. 1500ish stone cold, then 850-900 when warm. You could watch the idle drop as the temperature went up. This was all running fine. Then I did an engine swap.

I effectively only changed over the block and head as I took all the external parts off the new engine and put on all the sensors and external parts except for the knock sensor, O2 sensor and distributor. I even swapped over the hole engine loom and ecu to the original one. I put all this back in the car and started it, idle went up to 1500ish and dropped down slowly as the engine heated up and we bled the coolant system.

Car ran fine for a few weeks but then all of a sudden one day I was driving it I noticed the idle was up at 1500 when I pulled up to the lights. Thought something was odd but kept driving and got home. Took it for another drive a few days later and it was back to normal for a bit but then it jumped back up but then went back to normal on the same drive. Then I found it would rev hunt when stopping at lights but oddly enough it only did it a few times. Now it just stays at high idle when the car is warm.

So the current symptoms are low rough idle at cold and high idle when warm. Idle speed increases with engine temperature.

Things I've tried to do to find or fix the issues.
Rev hunting led me to believe it was a vacuum leak. So I checked all the vacuum lines but they are all connected and not damaged.
I tested for vacuum leaks using soapy water and pressurising the intake system through the idle valve. This found a significant vacuum leak in the ACIS plenum where it meets the manifold runners. So I sealed this up and noticed a slight drop in idle speed when warm. The gaskets were worn out and not sealing properly and because the manifold was swapped over along with the gaskets I went down the route of further vacuum leaks needing sorting. I've bought 3 new gaskets and installed them. No change.
I have changed out the throttle body too. This seems to rule out the TPS and IACV.
The next thing I am looking at is the engine temperature sensor for the ECU. When I unplug it at cold I get no idle speed change and neither when hot. The engine check light comes on when it's unplugged, as it should but not when it's plugged in. Resistance testing puts it at 2.2kohms at 22°. 20° is meant to be 4kohms and 40° is meant to be 1.3kohms. 80° measures 220 ohms. It's meant to be 0.37kohms. From testing Olaf's engine by unplugging this sensor the idle changed when it was cold so this points me toward a temperature sensor issue.

I have yet to check the ECU PCB and components, I'm not getting any codes either. There is 12v going to the IAC outside pins RSC and RSO so the valve is being controlled to some degree. There is always lots of air going through this valve and restricting it will bring the idle down to normal.

Is there something I am missing? Any suggestions would be very helpful.

[Dell'Orto]

Replace the CTS and see how it goes. These run a wax stat type idle up valve?

[GDII]

What's the CTS? All these acronyms Nah just the electronic valve. They do run coolant to the valve housing but this isn't what it's for.

EDIT: I assume CTS is coolant temperature sensor? I had one but gave it to a mate. Need to get another one and test it.