Sticking throttle

[Labbo]

I have a 2007 Precedent that has a sticking throttle. When I let off the gas the throttle still stays partially open and the engine backfires. When I step on the gas there is a delay before the throttle opens. I have replaced the cable and tried running it through different locations and changed the throttle return spring. Nothing seems to help. Any help before I bring it to the shop would be appreciated.