1990 Chevrolet Lumina

I have recently acquired a 1990 Chevrolet Lumina 4 cyl. It has some definate problems, need help figuring what to have checked. It is very weird!
When it is cold outside it mostly runs very well. But When the temp outside is over say 70 degrees the check engine light comes on, when the light comes on I lose the speedometer, odometer, and it runs rough and will die when I stop. When the light is not on or goes back off it runs fine. Also, I do not have reverse anytime. The trans works great in every other way just no reverse. When I put it in reverse it is like you have told it nothing, no change. Please help. Have a 15 yr old that wants to fix up the car and drive it, however I have a limited budget to do this on. Mileage is at 66000 but does not work all the time.

Thanks