Just an update, I've followed 07GTS's advice and just seen whether I can narrow down after how many hours sitting cold will it sputter as it starts, and so far I've let it sit without starting it for 9 hours , and it started fine after sitting idle for 9 hours, so then I let it sit for 10 hours cold without touching it again, and it still started fine, and now I've done an 11 hour cold start and it still starts fine after sitting there idle for that long, and now I've tried 12 hours to see if I can pinpoint a time window where it's happening, and it's still starting fine, and beyond 12 hours I'm not sure how much longer to try and leave it sit, and I've started a case with Holden Customer Care after finally getting a number where i can speak to someone, because when I first tried contacting them it was through the Holden website, and it basically kept looping me back around and referring me to my local Holden dealer, which wasn't what I was wanting seeing as though they've already looked at the car.
I know a lot of people blame bad fuel with things like this, so I made a concious effort to not immediately blame fuel quality, especially when it was only doing it on a cold start each day, and then running fine for the remainder of each day, and this might just be weird coincidence, but even though I normally only ever fill up with 98 octane fuel, and I usually try and stick strictly to service stations where all of their equipment is new, lately I've been using a particular local BP servo after they upgraded all of their bowsers and added 98 octane fuel on all of their pumps (the odd thing is that me using this particular service station roughly coincides with when all of this started up, and the more I thought about it, even though they upgraded everything above ground, that everything below ground is still all essentially the same, and they might have caused some sort of contamination or something when they put the new pumps in, or just some sort of humidity is getting into their fuel tanks or something, so I just decided to switch back to the service station that I'd normally used, and filled up there, and it's after that when I've been doing these timed cold starts, and I would've thought that it would've definitely did it somewhere in that 9-12 hour range of sitting cold, and it hasn't done it once, and in fact has started perfectly, and I've now stretched it as far as 12 hours, and it still didn't sputter on a 12 hour cold start, and if it doesn't do it after that amount of time, then maybe it's a problem with the fuel at this particular servo, and it's generally alright in normal use, but after its sitting for a certain amount of time it's just causing enough of a problem to make that happen.
It's just odd that I've been trying to make that behavior repeat, and been very strict with how long I let it sit for (9, then 10, then 11, and next will be 12 hours), and I haven't been able to make it repeat, and the only thing that's really changed of any significance is that I've changed back to the service station that I used to use, so it's still running on 98 octane, just from a different servo.
I'm gonna be super pissed if it's all been because of bad fuel coming from that servo, and if that's what turns out to be the problem then I'll be ringing BP's head office and letting them have it, because that's just terrible, and could be causing people all sorts of problems like burned out fuel pumps and things like that (after all its already cost me hundreds of dollars and no one, including the local Holden dealer has a clue as to what's causing it), and literally the only thing that's changed since it was sputtering on a cold start and now, is that I've switched back from the BP servo that I'd been using to fill up with 98 octane fuel, back to the service station that I'd been using up until a month or 2 ago, and now I'm convinced that it is/was a crappy fuel supply, because I went from being able to repeat it without trying, to not being able to repeat it at all now with letting it sit for 9, 10, 11 and 12 hour stints.
I'm not sure why bad fuel would cause that behavior only on a cold start each day, and then be fine from there, and especially why it'd be happening with a premium fuel like 98 octane, and the only thing that I can think of is that of is that they've somehow messed things up when they fitted all of their new pumps and stuff. It's just crazy, because I would've thought when they replaced all of the equipment above ground, and ran a dedicated pump for 98 octane fuel to each of their bowsers, that they would've made sure everything was right where it hooks up underground, but it seems like they didn't, and it's really pissed me off, because I could've potentially fried a fuel pump or something like that all because of sh!ttty fuel from a company like BP. I feel like ringing them and just blasting them, and showing them how much they've cost me over sh!tty fuel