Other ideas from the fox body forums. I looked them over and it sounds like decent advice. Lots of it would be a gradual onset. What's the owner have to say about the car?

http://www.allfordmustangs.com/forums/2-3l-tech/65135-1989-mustang-lx-2-3-goes-dead-when-cold-put-gear.html

http://www.stangnet.com/mustang-forums/701244-dies-when-put-into-gear.html

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95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)