I wouldn't use the trim on controller to adjust the idle. It's probably completely out of adjustment. If he has been messing with that screw the carbslide could have popped out of its track. I personally would put everything back to factory settings. And then start over rdrom there. But don't...
Welcome to RCT. What engine does your slash have in it. The trx engine usually have a slit movement to the engines while in idle. Is this a new nitro or one you have had ?
Like my 2.5 has slight jump to it in idle