Diesel. Runs perfectly + starts instantly. Unless warm!

[LunarOne]

Sounds like an engine temperature sensor might be kaputt. The car might be delivering too much fuel if it thinks the engine is cold but is actually warm. I saw a similar problem on a Diagnose Dan video, but it might have been not starting when cold. I can't find the video now as his videos have useless descriptions!

[Scrump]

What happens when you unsuccessfully try to start it?

[Rozzers]

It will probably be a failing crank sensor

[Limpet]

Could honestly be any number of things. Clearly an intermittent fault so suggests perhaps a wiring issue, or a sensor starting to fail, but it’s pure guesswork really at this point.

Probably worth getting a decent garage (not a dealer) to run some diagnostics. If they can catch it doing it, they will be able to nail this fairly quickly. If they can’t catch it or reproduce it, there may be stored codes that provide some clues.

[GreenV8S]

Scrump said:

What happens when you unsuccessfully try to start it?

^^^ This ^^^

Impossible to guess without knowing the symptoms.

[StephMurphy]

Scrump said:

What happens when you unsuccessfully try to start it?

Just turns over but does not start.

[StephMurphy]

Battery newish and fine.

[Matt_E_Mulsion]

Rozzers said:

It will probably be a failing crank sensor

I'd be tempted to try this too.

[stevemiller]

Matt_E_Mulsion said:

Rozzers said:

It will probably be a failing crank sensor

I'd be tempted to try this too.

Had this or was it the cam sensor? Once changed never reoccurred. The cam sensor only monitors the first compression timing. It was the cam for me confirmed!

Edited by stevemiller on Sunday 13th September 10:20