2000 Ford Explorer AWD Eddie Bauer idle problem

Mileage is about 125,000; 5.0L V8
The car dies out immediately after starting, unless you keep your foot on the gas. It revs fine, but take your foot off the gas, and it dies out. It died 8 times trying to get out of the driveway. Once it gets going down the road, it will idle and start fine for the rest of the day. When I try to start it again the next day, the same thing happens all over again. It just does not want to idle. I had it to a mechanic but of course the problem could not be duplicated since the car had just been driven. The check engine light IS on and has been for quite a while (I thought due to a different problem). The idle problem began a few weeks ago. Could this problem be caused by the idle control valve or would you suggest I take it to a Ford dealership to be put on the diagnostic machine? Thanks for your help!