I have an 1987 fox 5.0 and for some reason when my car starts to warm up it will either die at lights or will dive from 750rpm's to 500 rpm's over and over until it dies. When im on the gas it runs great. Can you lead me in the direction of what could cause this?

Thank you

 

Vacuum leak, or idle air control valve.

 

run a koer /koeo test first and check for codes

 

Having the same problem on my 88GT. I did a koer /koeo test and found a code 41 (lean code from the right side bank).I found that my power brake booster was hissing when I had the brakes applied. So I took the vacuum line off the booster and blocked it off. I want to go to none power brakes anyways. I like the feel better. I checked for other vac leaks and I do not seem to have any. The car is better but not all there yet. I think I need to clear the code. I am sure it is still in the system and making it run rich.
I am going to test the idle air control valve next as suggested above.