1999 saturn sl: changed spark plugs and wires. Ran good until warm-up then just chugged along. Catylitic changed 1/12 years ago...won't pass emmission test

If I crank the motor while it is st ??????? Probably ignition module . When it shuts off check for spark .

You need to run a fault code test on the electronic engine control module. You can learn how to do that here

Just check the air intake tube for splits & clamp tightness 1st. You may also want your airflow sensor tested

Done cars have a kill switch if they are low on oil. Check your oil. If the oil is good, it may be the ignition switch.

i ran in to a similar problem years ago , the spark plugs were bad ,old,and weak.be sure to use delco plugs that are specific to that engine

check timing belt!! good luck!!

Try make sure the plugs are good and the wires are good. Also try some Guaranteed to pass engine formula they reimburse you if you fail depending of course if you are in good mechanical condition.

Have you checked if your getting spark. You can do this by removing a plug and having someone hit the key for you. watch the spark plug don't touch it or you will get zapped. If you see a strong spark you should be good. Do this for all plugs. Alternatively you can try the crank position sensor this should be mounted between the intake manifold and the starter. Follow the wires to the location and unscrew the sensor.

If that is not the problem and your getting spark and gas to the cylinders. Let me know

It was the coolant temperature sensor. It was telling the car that the coolant was always cold, therefore when starting a warm engine it was being flooded. $$$

I DONT KNOW FOR SURE BUT I WOULD REPLACE THE M.A.S. AND THE 02 SENSORS. (IF MONEY IS AN ISSUE TRY CLEANING THE M.A.S FIRST)