First Start Issue - '97 Bathurst

Hi all,
 
I have been putting up with a first start issue for a while now, slowly trying to figure out what is causing it. The car is daily driven.
 
Car:
1997 MR2 SW20 Bathurst
3SGE Gen3
 
Symptom:
First cold start after sitting over night the car will stumble with low idle for 30 seconds before idling correctly. However I can turn the car off instantly and restart and it will run perfect. As the colder months arrived the car was starting perfectly first time every morning, now the hotter weather is back the car is stumbling on first morning start.
 
Things I have tried:
New leads
New distributor cap
New rotor
Spark plugs
New Coolant temp sensor
Intake temp sensor (borrowed from another car to test)
New Oxygen sensor
Cleaned the throttle body
Checked Idle control valve
Checked and replaced the idle control valve sensor (old one was still functioning within spec)
Fuel pressure checked
New fuel filter
Injectors cleaned and serviced, no leaks
 
Note: The car also has had it's major service during winter.
 
Edit: Car throws no error codes
 
Probably other things I have missed. I will add to the list when it comes to mind.
 
Any ideas/checks would be greatly appreciated.

I have tried resetting the ECU on other occasions but I will try it tomorrow morning right before I start the car. My next thought was to borrow a 'working' ECU from another club member and see what happens. I have checked over my ECU and I couldn't see any leaking capacitors.
 
The car throws no error codes.
 
 

That's interesting. I have spoken to the other Bathurst owners in the club and they also get the rare stuttering/stumbling start up. It started happening to me years ago on the rare occasion (I was using caltex 98oct fuel, swapped to BP 98oct and problem went away, so I thought it was fuel related) so I never really thought much of it.
 
Since it's happening more frequently (every morning) now. I tried filling up with different 98oct fuel brands but still happening.
 
3SGE Gen3 doesn't have a cold start injector. I believe the 3SGE Gen2 and 3sgte models have the cold start injector.

Me to, same issue. Like Joel changed from caltex to shell fuel and went away for awile. Doing it again now. Wondering if it's just a batch of **** fuel as it's all imported now.

I had this with my 3SGE gen 2, my brothers ST246 Caldina also has the same intermittent problem. I never found the issue, simply swapped in a 2GR

I tried resetting the ECU right before starting this morning. No luck.

Mrskylighter
I don't think this would prove anything but could you unplug the O2 sensor and start it from cold? It will use default values instead.
 
Reason i don't think it will have any effect is because I don't believe the ecu would use the sensor during cold starts because it has to be warmed up (heated sensor) for accurate readings. 
 
Might be worth a shot and its easy to unplug??? 
 
Edit: I see you have replaced yours Lumix but still might be worth doing if you haven't tried it already.

Yeah I replaced mine last week. No harm in trying it though. I will do it over the weekend so I'm not rushing in the morning before work.