I replaced the header on a 99 4.0 hooked everthing back up as it was, new gasket, all the wiring and plugs hooked up, vacuum lines all back to where they belong, and when I fired it up it runs wide open. Any other ideas?

 

Someone else has a post on the same exact issue, not sure if he found a solution but I know I saw it on here the other day. I can't find THAT thread but here are some related ones. Looks like it may be a vacuum leak on the intake.

https://www.cherokeeforum.com/f2/87-...rop-off-46010/

https://www.cherokeeforum.com/f2/hig...tart-up-17718/

 

What header did you use?

Most often it's a vacuum leak causing the high idle after an intake/header replacement.

 

That was me that had that problem. We had the intake sitting on top of the alignment dowels. Take the intake off and see if there are indentions/ scratches around the hole for the dowel in the intake. If so you did the same thing i did and just need to align it so it sits in the dowels not on them.

Here is my orignal post so you can see if your problem and my problem sound similar. https://www.cherokeeforum.com/f2/reving-moon-48922/

 

Take your foot off the gas?