My 92 mustang 5.0L is running bad when i rev it to about 2500 rpm the low coolant light comes on and the check engine light come on. then the rpm will drop and run fine untill the next time I rev it to about 2500. The code that i am getting is 21 with the engine running and no codes when the engine is off.

Thanks Sean

 

aldo getting two other codes: 41 and 91

Thank Sean

 

check your ignition module