Problem starting 99 Golf when very hot outside or raining. I've recently changed the distributor Cap in which has help with the in consistent idle but this problem remains. I'm guessin it's the engine heat sensor or the spark plug wires?

Any feedback would be appreciated.

Optional Information:
1999 Volkswagen Mk3 Golf 4 Cyl 2.0 Gas

Already Tried:
Changed distributor cap and spark plugs