91 Mighty Max Cold running issue
 

I got a 91 Mighty Max and when the motor is cold it kicks out a CEL, having tested to see what it is since i dont know how, and it will go to about 7mph and cut out, then ill shift and it will go another 7mph and cut out, to the point where if i go over 35mph in 5th gear it cuts out. but after the motor gets warmed up it runs normally. Any idea how to fix this?