I just installed a stock LT1 throttle body on a LT1 corvette that was modified to a 52 mm by Xtreme FI. It does not seem to stick when the engine is off. But when the engine is on and I roll into the throttle it sticks around 2500 RPM. When I turn the engine off the thottle moves to the idle stop. It seems like engine vacuum is pulling the blades open. Has anyone seen this before? Is there a fix?

 

I would say there is something wrong with the throttle body. I also bore LT1 thorttle bodies to 52mm and have done the corvette style many times.

They have a much stronger throttle return spring than the F-body style throttle body. The Corvette spring setup is a dual spring and can be easily setup incorrect making the tension weak. Do you still have the stock throttle body? If so how does the throttle shaft move compaired to it? It should have no problem at all pulling the blades shut.

 

I sold my old thottle body already. How much would you charge to fix it if I sent it to you?