[Tannaton]

I don't think you have mentioned (unless I missed it) whether the car is under warranty or not, I'm assuming not as it's been to an Indie, but if it is you should continue with Volvo.

I've had a theory for a long time that cars are so well engineered now that it is very rare for sensors, injectors etc. to fail and cause problems like this, usually it is another problem - like the one you described with an ill fitting seal.

For example, if just fixed an old Ford Ranger pickup I bought recently that's been to and from the main dealers and other garages (with the previous owner) with a random hot starting issue - thousands have been spent on it in the last 18 months. Assuming it to be a fuel pressure regulation issue (in the absence of any codes) I stripped, cleaned and re-assembled every part of the fuel system that can influence system pressure. I found a spec of plastic in the over pressure bleed valve on the fuel rail, and a few bits of muck elsewhere. I can't be certain what made the difference as I did it all in one got but it's a different vehicle now, not only is the starting issue fixed it's a smoother, more responsive vehicle. No parts where replaced, just stripped down as far as possible, cleaned and re-assembled.

And I would suggest you do the same. I don't know much about this engine specifically, 99% of my tinkering is with diesel now but the change in behavior when it switches to closed loop as it warms up is a massive clue I'm sure and that does not point to injectors.

So I would be tempted to strip, examine, clean and check the whole fuel system (if you are able to do that) and see how is goes from there?

Next step would be to start looking at the real time data during warmup and running, i.e. fuel pressure, duty cycle, O2 etc.