1999 Jeep Wrangler REVVING

After changing out the exhaust manifold, the engine will rev at start and continue to rev until I shut the engine off (before it redlines). Any help would be great.

Sounds like you might have a vac leak at the manifold ( intake). Double check and makesure everything is connected. If it ran good before you started, you might have forgotten a hose or something.

make sure that the throttle cable coming through the firewall isnt hung up and that the throttle body is closed. if that is sitting fully opened then that will cause it to redline quick at start up. sounds stupid but could happen.

When I swapped mine out I had to replace the Idle Air Control Valve also. It wasnt revving as hard as yours but it would rev up to about three grand.