Engine REVs high at start after manifold replacement :confused: - JeepForum.com
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Unread 01-09-2011, 10:06 PM   #1
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1997 TJ Wrangler 
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Engine REVs high at start after manifold replacement :confused:

I just replaced the exhaust manifold on my 97 TJ 4.0. Whenever i start it now the engine just REVs like someone is stomping on the Gas. i'm not sure what would cause this but i ran into a couple other problems as i was putting everything back together that might be helpful in helping me figure this out.

When i put the power steering pump back on the bolts didn't line up through the bracket and into the intake manifold, so i had to unbolt the bracket from the block in order to get the power steering pump screwed into the intake manifold. then the serpentine belt would not fit around the power steering pump pulley, even when the idler pull/tensioner pulley was fully extended; i ended up having to use a pry bar to get the belt around the pulley and even then its still not completely on.

I'm assuming that when i put on the intake manifold i must've not seated it fully or correctly and that is somehow contributing to the immediate high acceleration when i start the engine. i've checked the accelerator cable and it's not stuck open at all, so i don't think that is the problem.

i'm hoping someone might know what i did wrong before i have to strip the whole thing down again. so any advice or ideas anyone could lend would be greatly appreciated.

oh, and using a torque wrench on those manifold bolts is practically impossible, i don't see how you're supposed to get a torque wrench in some of those tight fit spots.

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Unread 01-09-2011, 10:38 PM   #2
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Vacuum leak is the most likely source. Since you had bolt alignment issues, maybe the manifold isn't seated well.
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Unread 01-09-2011, 10:39 PM   #3
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That's the most common symptom of a massive air leak at the intake manifold. Re-check your work, either the intake manifold is not seated fully flush to the head, or you forgot to reattach one of the vacuum hoses. Use a drill to clean out the dowel pin holes in the manfold. Chamfer the holes too.

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Unread 01-10-2011, 07:18 AM   #4
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i had this happen the first time i replaced my exhaust manifold, and wound up cracking the intake. make sure the intake is lined up on the 2 dowel pins on block at each end of the intake. once you have the intake back on try to hold it flush up against the block and try to slide it STRAIGHT up, you should have about 1/8" of play up and down, if it comes up off the engine it wasnt on the dowel pins.
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Unread 01-10-2011, 07:25 AM   #5
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also i have found that using a u-joint in between the socket and extension (6 inch on the bolts closer to the ends and a 9 inch on the inside bolts) works best. reach under the intake with the socket/u-joint/extension (off the wrench) and put it on the bolt head and hold it there, then install the wrench on the extension and torque to spec. if you have someone helping you, have them get under the jeep with a flashlight to help you get the socket on the bolt head (also can have them stick their pinkey finger in the dowel pin hole to see if it is lined up properly)
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Unread 09-30-2014, 11:58 PM   #6
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I'm having the identical problem. I have already re-installed the manifolds for the second time and i still have the high revving at start up. My vacuum lines seem to be ok so i have to assume I'm not lining up the intake manifold properly. I looked at where the intake manifold seats on block and it is touching on the top edge but slightly off as you go down . I think the problem is that I didn't hold the manifold tight and square onto the block as I tightened the bolts . I assumed the manifold would seat square as I tightened it but its not happening . I'm going to try again and focus on keeping the manifold square onto the block as I tighten and also on those alignment pins . Regarding torquing the bolts i just torqued them by feel because like you said there's no way to get a torque wrench in that clutter. A friend of mine said that they should be torqued to about the same force you use when installing a spark plug . Something I did to help line up the lower bolts is I marked their location vertically on the valve cover so i had a target when trying to get them onto the wrench socket. I will let you know how I make out tomorrow.
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Unread 10-27-2015, 08:44 PM   #7
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yea this problem drove us crazy till we figured it out!
the dowel pins are the problem. We had the front one in ,but the rear one
Missed ,and it looks fine tightened all the bolts ,and when stared the engine
Instantly red lines.
To fix this ,take off the serpetene belt off, loosen all bolts on the power steering
Bracket ,loosen all intake bolts as far as you can without removing them,
move the intake around until the rear (closest to fire wall) goes on the dowel
And will not move up and down (if it moves up and down u are not on the dowel)
lightly tighten the 2nd top bolt closest to fire wall to hold it on the dowel, now
Check the front dowel and when no up and down movement snug a top bolt lightly
now that intake is on both dowels, start with the 2 lower center bolts and tighten,
Then top 2 center bolts and continue to tighten all bolts on the. Intake from the center
Out. Then tighten power steering bracket bolts and put the belt on and your done.
if you did it right it will idel normaly since the dowel pin is not holding the intake
Off the head and creating the massive vacume leak which causes the engine to red line.
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Unread 11-03-2015, 09:19 PM   #8
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02 tj 4.0

yah I hate exhaust manifolds just took me 2 and a half days to do. and back at it tomorrow same redline issue but I am going to follow what tab1977 said to do cause im not trying to do it all over again I am tired
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Unread 11-04-2015, 12:22 PM   #9
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You may also need to check your clearance between the exhaust and intake manifold. I bought the cheap accordion style and the bend on the front most tube was hitting the intake manifold. I had to grind away some of the casting that goes up to the hole that the power steering bracket mounts to on the intake manifold.
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