can't figure it out

[AddictedtoNITRO]

ok so I've tried fixing this problem numerous times to no avail. My buggy likes to stay at full throttle when you let off the gas. It ONLY does it when it's running. I think meatwad had a similar problem. so far I have changed the throttle servo, taken the ENTIRE buggy apart and cleaned and tightned with locktite every screw. No fuel line leaks. no air leaks in the engine. changed recievers and transmitters. changed battery packs.
I knoticed that if you remove the linkage off of the throttle the carb opens about 3/4 way. it slides very smooth. I have not yet put a throttle return spring on it because I never had a problem before and when I tried closing the throttle when it sticks open running it sticks! like the servo is saying nope not gonna happen. I'm thinking it has to be in the carb but idk. I disconnected the throttle arm and started the engine and it works fine so I figure it can't be 2 bad servo's lol.
It's beginning to really frustrate me
hope you can help
thanks
jeff