New LS3 crate Engine - Idles HIGH

[brgarris]

Just got my new LS3 525hp crate engine cranked and it wants to rev to 3500 rpm and then back itself down ~1000 rpm. The car just has headers and no exhaust right now, but i would assume that wouldnt cause the problem. Whats weird is that I can place the car in gear, slowly let off the clutch placing load on the engine and the car will lower idle to 800-1000 rpm. If I place the car back in neutral and tap the accelerator the idle will go back up a bit. I have no clue how to explain that. Any help out there?

[TomMLS1]

You have a vacuum leak. Plug the small port at the rear of the intake. The larger one should be your brake booster. There are also two ports at the front of the intake on either side of the throttle body, plug them, or use them...

T,

[martZ]

If you have the older style throttle body it will respond this way with the 525 ecu.