I have a 1993 silverado v8 5.7 and my rpms are going crazy when i come to a stop or if i have it in parking can someone help me with this problem

 

what do you mean crazy like is your motor loping meaning is it a rough idle and rpms are fluctuating like 100-200 rpms or is motor doing nothing wrong and the rpms are jumping into the thousands or what?

 

they go up n down from 0 to 100rpm untill the truck turns off the only way it satys on is if i step on the gas n break at the some time when i come to a stop

 

Okay well i would start simple. This could just be a dirty throttle body, so get you a tooth brush or a clean rag and coat hanger(be gentle) and spray with throttle body cleaner and clean it all out. Also, could use some new spark plugs and wires. Another question for you is the truck almost fighting to stay running or just a rough idle.