Micra K11 dies after starting

Hi all,

My partners got a Nissan Micra K11 ('02 plate) 1.0 manual that from time to time refuses to start properly.

Essentially you turn the key, the starter turns properly and the engine fires up nicely - however, as soon as you let go of the key the engine dies.

Now I know that the Micra has an issue with a faulty ignition switch, but that's only when the starter doesn't fire at all, this works fine and the engine starts, until you let go of the key when it just dies.

I'm also aware that they have an issue with dodgy throttle bodies/TPS, but I'm loathed to spend £100 to replace it unless I'm 99% certain it will fix the problem.

So, does anybody have any idea what it could be? Or what I could try to investigate further/rule things in/out?

Thanks in advance!