The Ford EFI is programmed to idle at ~1500rpm after a cold start for a few seconds, then fall back to normal (850 on my '88 T-bird 302). The 500rpm/dying thing is not normal. Your IAC (idle air controller) may be dirty or bad, and/or your throttle blades may need cleaning. Use throttle cleaner spray from a parts store on both. It's similar to carb cleaner but won't screw up the catalytic converter. Spray off the area where the throttle blade contacts the housing, & shoot some into the passages of the IAC. Also, wiggle the wire connector on the IAC. It may just have a bad connection, & sometimes wiggling the wires will restore it. If so, clean the connector contacts & coat them with silicone grease.
