1990 Pontiac Grand Prix - idling problem

The vehicle in question has about 250000kms on it, 3.1 L non turbo LE model. I started having issues when I was driving it, it would stall at stop lights. I took to Canadian tire and the diagnosed it as having two issue, the first was that one of the ignition coils was not firing, and the second was a possible issue with the map sensor, I replaced both. I decided to replace the spark plug cables as well. When the engine is cold it runs perfectly and is drivable, but once the engine warms up it stalls. The service engine light is not on (used to be before I replaced the map sensor and coil). I don't think its the fuel pump as it runs fine when cold, I am not sure about the idling motor. Any suggestions?