Engine cutting out only in the wet!!!

[David-polo9n3]

Alright guys having a bit of a problem with my Polo 9n3 2006 1.2.

Lately every time its been raining my polo will start and when reaching 3000rpm the car will start to drop and go into lower revs and bounce untill it dies. After this happens it wont start again until its dry.
Ive taken it to mechanics and they have did a diagnostics on it but no errors came up. Theres no water getting in the engine bay that i can see.

Anyone got any ideas or had this problem also ?

Cheers,
David