You can't rely on doc for another vehicle, and even various years of the same model sometimes differ - as it does with Aveo throttle body. TPS for an '08 is built-in to the TB and cannot be replaced. First try removing the TPS sensor connector and cleaning both sides, along with carefully inspecting all of the wires coming into it. If that doesn't help, next try removing the TB and cleaning as you were planning to do. Lastly, never buy parts from a stealership unless there is no other choice (which is rarely the case). Rockauto is selling TBs for the '08 for $100-200 USD, and you could also consider getting one from a U-pull, if there are any available where you live.