I had this problem on my car; turned out to be the coolant temp sensor. It's connected to a blue plug (looks like a fuel injector sensor) right in the middle of the block, below the inlet manifold. It changes resistance according to the temperature of the coolant, which in turn tells the ECU how much fuel to inject. Mine was corroded which resulted in the car running permanently on cold-start enrichment cycle, flooding the engine when trying to start from warm. The resistances should be as follows:
@ 10'C you should read 3800 ohms
@ 15'C you should read 3000 ohms
@ 25'C you should read 2000 ohms
@ 80'C you should read 320 ohms
Firstly make sure the terminals on the sensor and connector are totally clean, then if that does not solve it, as a temporary fix, and if you need to start the car when its warm you can unplug the connector from the sensor and bridge a piece of wire accross the connector's terminals (with the engine off.) This worked for me, though it's a bit of a hassle as you have remove the wire and plug it back in to start from cold.