It really sounds like the whole problem is that the idle is too high.
There are 2 things that will cause a high idle 99% of the time.
One is the idle screw being too far out. You should take the air filter off the carb and look into the carb and the slide when at idle should have about a .5-1mm gap set for the idle.
If that is set correctly check your low end needle as that's the second thing to look at. Having a low end set too lean will also cause a high idle that lots of times won't ever allow the engine to idle correctly.
Check and set the idle screw FIRST.
Then double check your high and low end needle settings and reset them to break in specs according to the traxxas manual. After this make sure to NEVER adjust the idle screw again and retune the engine. Set your high end first and then set your low end. Traxxas has a very thorough and detailed write-up on their site about engine tuning that should help you.
Here is the tuning page on traxxas.com:
http://www.traxxas.com/support/kb_se...l&cat=0&id=276
Also here are the factory carb needle settings according to Traxxas.com:
http://www.traxxas.com/support/kb_se...l&cat=0&id=450