Why do I have such high idle

[97on20s]

 

I have a 97 Silverado with a 5.7 Vortec and everytime I start the engine the idle jumps to about 2000 rpm for about 5 seconds then drops down to normal. When I put it in gear it does the same thing, I can feel the truck wanting to jump forward and have to hold the brake to keep it from taking off. It just starting doing this about a week ago and my diagnostic port doesnt have any power going to it. The truck has been butchered to say the least. Is there anyway to find out why this is doing that aside from changing the computer, that will be later on down the road. Thanks for any help, sorry for the long story.

[mjgjr72]

I have a 97 Silverado with a 5.7 Vortec and everytime I start the engine the idle jumps to about 2000 rpm for about 5 seconds then drops down to normal. When I put it in gear it does the same thing, I can feel the truck wanting to jump forward and have to hold the brake to keep it from taking off. It just starting doing this about a week ago and my diagnostic port doesnt have any power going to it. The truck has been butchered to say the least. Is there anyway to find out why this is doing that aside from changing the computer, that will be later on down the road. Thanks for any help, sorry for the long story.

 

<{POST_SNAPBACK}>

 

 

posible vacum leak, try spaying aroung the throttle body base with some carb cleaner to see if the gasket cracked, check for cracked of disconnected vacum hoses