Insignia 2.0CDTI - Hard to start with "warm" engine.

[mucklestone]

I have a really weird starting issue with my insignia. It starts perfectly when the engine is cold, and it starts perfectly when the engine is hot. But when slightly warm it will barely start.

For example, I can start the car from cold fine, but if drive a mile and switch off it becomes extremely hard to start, often taking 3 cranking attempts.I have tried searching and the other suggestion I have found is weak battery struggling to start it because hasn't had chance to charge up again. However it doesn't feel like it, it cranks fast and I have had a voltmeter connected for a month and the battery seems fine.

Even during extended cranking the voltage stays quite high.

Any advice or suggestions would be appreciated!

It's a 2013 2.0CDTI (160) hatchback with 112k on the clock. I have had it from new and everything is original (original turbo, original injectors, egr, dpf etc. etc.)