RealDrJ

First of all it's a 2000 Cherokee classic 4.0 4wd. It's been idling rough and finally the engine light came on. Drives fine as soon as I give it some throttle. Code was a misfire on cylinder 2. I started looking at it tonight and found a crack under the throttle body inside the intake manifold. It isn't cracked all the way through. Anyone else had this issue or know if this could be leading to the rough idle/misfire.

97grand4.0

looks like maybe you had a backfire there and it burned for a while. Things sure look dirty there. A little grit on the throttle plate will prevent it from idling right, and likely the IAC is either dirty or shot too. That could cause rough running. Start with some good quality carb and intake cleaner spray.. Never seen a crack like that though, couldnt say if it affects it or not, doesn't look good for sure. Not sure what to advise you there.

RealDrJ

Thanks, I'll get the IAC out today and see how it looks. I had the cracked head about 30k miles ago and got that all squared away and it has been running great until last week. But it has been really slow to start on cold days so I'm hoping to get rid of that issue while doing all of this too.

BillyBoy

I think the question might really be... "should I replace this?" The reason I ask is what if it cracks off and a piece gets sucked into the engine? Boneyard, new one asap. That's my vote. Other things can break off and not cause catastrophic damage. Just my .02$

BlueRidgeMark

That may be a casting flaw, not a crack. If it were a crack, I'd expect more problems than just a miss on #2 and a poor idle.

Programbo

Yes that's what it is. I get '99+ intake manifolds at the junkyards to sell all the time and almost all of them have this "crack" on the inside. I guess something about the indentation in the intake during manufacture causes it to look like this on the inside. If you look under it with a mirror or whatever you will see the outside is fine.

RealDrJ

You guys nailed it, not an actual crack. Took out the IAC valve and it was filthy so I gave it a good bath and the idling got much better. Now to track down the vacuum leak. Thanks for all the input.

BillyBoy

I heard you can spray some start getting fluid on the connections and the engine will Rev higher when you find the leak... just sayin.

RealDrJ

Well great news. It wasn't a vacuum leak. Apparently the new head I put on last year has warped and is leaking between cylinders 2 and 3. New head will be covered under warranty but labor will be fun to pay again.