Start stop immediately(99 Crown Vic.)

Hi.My 99 CrownVic. Starts fine but will die immediately.It will run slightly rough with a little gas.Yesterday morning it ran a little rough for a minute but was fine. Checked everything fluidwise and looked fine.Thanks

The most common cause of this behavoir is a worn-out IAC (idle air control) valve. The PCM controls idle speed with the IAC valve o modulating the air allowed into the intake manifold. If you can get it to run with just a tiny bit of pressure on the gas pedal, it is probably the IAC. You might also get it to work for a while by tapping on it lightly. I would estimate about $100 for the part. It is easy to install. You can find some pictures at