70 C10 LSX swap question

[ClassicGuy]

Hello everyone,
I have a 70 short bed that I recently put a 5.3 Vortec motor in. I bought a new harness and had the computer flashed. I made sure all connections are plugged in and lines are all tight. I start it and it immediately revs up really high and back fires. Then it goes to normal idle for about a minute then revs up again and just stays there. I checked all vacume lines and there are no leaks. My harness is hooked up to a good ground. I did notice that the Evap Solenoid is missing and there is just a hole in it’s place. Could that be the cause of it? Any advice is greatly appreciated as this is my first swap. Thank you

[crazy longhorn]

Some of the trucks , did not have that evap solenoid...(tin cup that pushed in with a bolt to hold it down. Get your best bud , or wifey out & stick a thumb over the hole.....fire it up & see if that takes care of the problem Longhorn

[mattfranklin]

Originally Posted by crazy longhorn

Some of the trucks , did not have that evap solenoid...(tin cup that pushed in with a bolt to hold it down. Get your best bud , or wifey out & stick a thumb over the hole.....fire it up & see if that takes care of the problem Longhorn

I'd second that. A hole like that acts like a vacuum leak. If you're working by yourself figure out what makes a good substitute for a thumb. Rubber plug, big piece of duct tape, or whatever.