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I just replaced pistons, lifters, pushrods, and head on a 1999 Jeep Grand Cherokee. It started right up, but the RPM went to redline.

I checked throttle body components, the linkages are OK, but the valve plate is not opening.

What can cause this?

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It sounds as if the intake manifold is not sealed properly. The large intake leak will force the engine to redline instantly once started.

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