Engine dies at startup

I have a 99 Windstar 3.8 LX with 108,000 miles. The IAC was replaced last year at 94,000 miles. Lately, the engine has been shutting down upon startup about 50% of the times the car is started. I have to press the gas a few times immediately upon startup to prevent it from shutting down. Once it's stable, it doesn't shut down even during idling.
However, it chokes when it runs. It jerks a few times as if it's about to shut down but then stabilizes again when I press on the gas pedal.

Need suggestions as to what might be the problem.

Does this happen at hot start and cold start?

Is the MIL light on? If so, you should have the codes read. Some auto parts stores will do this for free.

If thie MIL is not on, you can induce it on using 12Ounce's method... Removing a vacuum line (temporarily) to get a misfire. Once the light is on replace the vacuum line and take the vehicle to a place that will read the codes for free. He does this because they will only read the codes if the MIL is on (even though there can be codes stored when the MIL is off).

A malfunction with the TPS, the IAC, the MAF, or the EGR can cause idling problems. Your problem seems a bit different since it seems to only occur when the engine is first started. The codes will help give a better idea of where to look.

Check the spark plugs to see if there's no oil/carbon deposit on them.
Did you put fuel additive in your gas tank recently? Like gas treatment, or gas stabilizer?