Check the air gap in the ETC first; the two contacts should stay open while you are "giving" it throttle and they should be closed "touching" at idle.
To check it:
Take the black cover off the thumb throttle housing. Inside you will see the lever with 2 grey wires going into it. On one end is the pivot point for the thumb throttle, the other end pulls the throttle cable. Next to the cable pull is a set of springs with a square-ish hole next to them. Inside the hole, you'll see the contacts for the two grey wires. At idle, not touching the thumb throttle, those contacts should be touching each other. Next, slowly push the thumb throttle like you're giving her gas. Those contacts should separate to about 2mm and STAY separated that distance all the way through til you hit full throttle position. My guess right now, is that they are staying open while in the idle position too, which causes the throttle safety to activate; killing the bike. IF that is the case and they are staying open at idle, then follow these procedures to adjust it so they close at idle:
1. Slide the boot back far enough to expose the inline cable adjuster sleeve and loosen the adjuster locknut.
2. Remove the (4) screws and cover from the RH control.
3. With handlebars centered and wheels pointing forward, slowly turn the adjuster sleeve counter-clockwise (out) just until the gap is removed between the throttle arm and the throttle arm stop (see illustration below).
NOTE: While moving the adjuster sleeve, “flip” the throttle lever slightly to remove slack in the cable.
4. Turn the cable adjuster sleeve clockwise (in) 1.5 - 2 turns; tighten locknut and reinstall boot. After this adjustment there should be .079-.118” (2-3 mm) gap between throttle arm and throttle arm stop.
5. Reinstall the RH control cover and ensure the O-ring is properly in place. Securely tighten the (4) screws.
6. Place the vehicle in PARK and start the engine. Turn the handlebars from full left to full right while listening for any change in engine speed. If engine speed changes, loosen the locknut and turn the adjuster sleeve clockwise (in) an additional 1/2 turn and repeat this step.
Hope this helps ya! And congrats on getting her back atleast!