Cold starts will rev down and up and stall when put in gear

Hi,

1992 Aerostar, 3.0 Litre, auto, 300,000kms.

A couple of months ago when starting the engine cold, actual outside temperature does not matter, the engine will start just fine but then if I lift my foot from the gas it will rev down to the point of almost stalling then rev back up again and do this over and over again. Also when I drive shortly after the cold start the engine will stall at stop signs and is very hard to get started again.

Once the engine warms up it generally runs fine and seems to idle well.

If I park the van for a few hours, 3 or 4, and then go to start it, the above rev down rev up scenario repeats itself.

Thanks for any info
Michael