Engine unhappy at initial rev increase

After finally getting the Ghia drivable we went on a short drive last night.  The engine was beautiful - surprising as it probably hasn't been running for more than a few minutes in the last 6 months or so.

However, we stopped off on the way back home to pick a few things up and the engine trouble started.

Basically, the engine will start and idle perfectly.  But when I apply gas (even when standing out of gear), the engine splutters and almost stalls.  If it doesn't stall and I can increase the revs it runs fine again - keeping the revs up high managed to get me home without stalling too much.

This morning I tried the engine again and it seems fine.

Could it be a problem with the engine being hot? Or maybe something to do with water in the wrong place (we drove through some huge puddles as it'd been raining very hard yesterday)

Any thoughts would be appreciated!