Slowbrick
If its LH2.2 it will have the idle screw. Just turn that shit till it idles. How low does it idle though? Mine idles ~750 - 650 depending how cold it is outside. When I had the IAC unplugged I just set it to 850 and it was happy as.
GingerNinja
The car idles fine at around 850ish but if you put it in gear and try to take off it's not happy. I'll increase the idle speed to 1000 and see if it helps.
jamesinc
Based on what you've looked at already, my money is on either a faulty ECT or maybe you've simply slipped a tooth on the timing belt.
GingerNinja
Looks like a dodgy MAF was the main problem. Thanks to @volvodriverman for dropping off some spares for me to try. It doesn't want to idle when it's properly cold though. I tried driving tonight when it was about 5 degrees out and it wouldn't idle. It would start at about 1000 and then drop to ~400 and then jump to 1500 if it didn't stall before that. I might swap out the IAC to see if that helps.
It also has inconsistent boost. Sometimes it will reach 12psi, but often it will only get to 7 or less. I've replaced all the cracked hoses and checked for leaks and even swapped to the spare intercooler. When I pressurise the intake and spray a bit of soapy water it seems to bubble from the gap between the CBV and the compressor housing. Can you replace the o-ring in there? it seems to be baked pretty hard. Or is it more likely to be the valve no sealing properly? I think the turbo is a 12c.
Slowbrick
A 12b will have the Pierburg CBV. I believe you can still get replacements for it.
volvodriverman
You'd played with the idle screw yeah? The base idle was set correctly on this car & was always rock solid. I can't think of the process exactly off the top of my head but will get back to you, this will likely be the idle issue.
Boost issue is odd, once again, always consistent. Sounds like the old girl didn't like moving south again!
jamesinc
Sounds like a new CBV is in order.
My 740T used to dislike cold weather, though it would smooth out after a minute or so warm-up. Is yours doing the same or is it just constantly hunting idle?
GingerNinja
It takes a couple of minutes to warm up and then it's fine but sometimes it will stall if it's really cold. I'll check the manual for setting the idle again.