Engine races to redline when started

[Tyn Pow]

I replaced my cracked manifold with some pacesetters this weekend and went to fire the old pile up and the engine kicked in and kept winding up as if my throttle was stuck wide open.  Tried restarting a few times and everytime it just wants to rev out to redline.

Checked my throttle linkage first, its all good, then all my vacuum lines and harness connections and they all seem fine.

Removed the air intake hose and had someone watch the throttle just to be sure as I started it and the blade stayed closed.

Then replaced my TPS with no luck.  Could it be the IAC?  Can an open IAC valve even flow enough air to let the engine wind out?

Any other ideas?  99 XJ w/ 4.0 and auto

[hps4evr]

this happened to me the first time i installed and aftermarket header on a 4.oL. sometimes if you dont have the exhaust manifold sit perfect against the head it will misaligne the intake manifold on the dowel pins that align in to the head. in other words you have a massive vacuum leak at the intake manifold. it happened to me at the back of the intake, closer to the firewall. check with a light at the back to see if its sealed properly. this is where i would start first.

[Tyn Pow]

this happened to me the first time i installed and aftermarket header on a 4.oL. sometimes if you dont have the exhaust manifold sit perfect against the head it will misaligne the intake manifold on the dowel pins that align in to the head. in other words you have a massive vacuum leak at the intake manifold. it happened to me at the back of the intake, closer to the firewall. check with a light at the back to see if its sealed properly. this is where i would start first.

Hmm, that crossed my mind since its the only other place air could come from but good to know from somone who experienced it.

Thanks

[apeman]

Not sure if you just bolted everything up with a dry gasket or not but i always use Loctite Copper Silicone on each side of the gasket, and let it skin over for about 20 minutes or so...this prevents any leaks in either the intake or the exhaust...and you end up doing the job once..