Any HP tuners ran into this. Everytime I try to do the simplest tweek to the stock tune the car revs up to about 2000rpm @ start-up and the idle surges between 800 and 1000. I put the stock tune back....everything is fine. Add 1* of timing @ 5000rpm...same problem. Then I downloaded a tune from a board member that wasn't stock..and the car cranks and idles fine. But if I tweek that tune ANY, same problem. The shop that did my dyno tune said they have tuned tons of LS1's and never seen this before. Any insite would be greatly appreciated.