Problem keeping the car cranking. Please help!

Ok. All I have done is replace spark plug wires. They are in the correct firing order and I can start the engine. The engine starts then dies right away. HOWEVER, I can keep the engine running as long as the accelerator petal is depressed. As soon as I let go of the petal, the car dies. This is for a 1.8L SOHC (1990 i think)

The alternator is only 1 month old and the battery is only 8 months old. I've checked timing belt and it looks ok too. no skipped teeth. The headlights are still bright so the battery has a really good charge. I just want to know what else could be the problem. Anyone care to presume why the car is acting this way?