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  #1  
Old December 7th, 2016, 18:08
shmicah shmicah is offline
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Fast mechnical tick/whirl from intake manifold

Was digging around for vaccum leaks on the 99 XJ.

There is a very distinct mechanical clicking/whirling sound that is intermittently happening somewhere near the air intake of my intake manifold. It almost sounds like one of those sensors there.

It'll make the nosie for like 10-15 seconds, then stop for a bit, then randomly start again. It makes a very consistent rhythmic click - like a mechanical switch opening/closing very fast.

All my googles lead to exhaust leak or lifter tick. I have the lifter tick so I know its not that. I don't think its exhaust leak either as my RPMs are normal, and the car drives wonderfully. I just have very bad cabin vibes when sitting in gear with brakes on.

I took a hose and listened and am very confident it is near the TPS. Are any of those intake sensors known to have a relay or make this noise?
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Old December 7th, 2016, 20:15
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lazyxj lazyxj is offline
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Re: Fast mechnical tick/whirl from intake manifold

A loud fuel injector?
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Old December 7th, 2016, 21:12
ID96XJ ID96XJ is offline
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Re: Fast mechnical tick/whirl from intake manifold

Could it be the IAC?
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Old December 8th, 2016, 06:25
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90xj06 90xj06 is offline
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Re: Fast mechnical tick/whirl from intake manifold

the iac is a stepper motor and when they get stuck they do make click like noises. but the iac is so small im not sure you could hear it.
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Old December 8th, 2016, 08:12
shmicah shmicah is offline
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Re: Fast mechnical tick/whirl from intake manifold

Quote:
Originally Posted by lazyxj View Post
A loud fuel injector?
Possible but it doesn't sound like its coming from there. I know its hard to be confident of that though. I pulled each FI and the XJ stumbled every time so they are all working correctly. Next time I hear the tick I'll do it again and see if it stops.

Quote:
Originally Posted by ID96XJ View Post
Could it be the IAC?
Quote:
Originally Posted by 90xj06 View Post
the iac is a stepper motor and when they get stuck they do make click like noises. but the iac is so small im not sure you could hear it.
IAC is definitely in the area I am hearing it. It is very faint and I have to put my head up to the manifold to really hear it. You would never hear it with the hood closed or from the cab.

I recently had the manifold removed and sitting the garage for ~6 months. Perhaps the IAC got dirty or gummed up? I cleaned it a while back, but didn't really bother cleaning again before throwing it back in.

I'm just tracking down a rough idle, and I know my brake booster is bad so hoping its just causing a minor vaccum leak. So I will tackle that first and if it doesn't make a difference I will troubleshoot the IAC. My only problem with that is how smooth the RPMs are.

Thanks yall

Last edited by shmicah; December 8th, 2016 at 08:31.
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Old December 8th, 2016, 08:16
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dan1977p dan1977p is offline
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Re: Fast mechnical tick/whirl from intake manifold

Does the rough idle change if you plug the brake booster line? If not, that's not your vacuum leak.
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Old December 8th, 2016, 08:16
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Re: Fast mechnical tick/whirl from intake manifold

iac does control the idle speed and if its all gummed and not working that could be a problem.
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Old December 8th, 2016, 08:26
shmicah shmicah is offline
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Re: Fast mechnical tick/whirl from intake manifold

Quote:
Originally Posted by dan1977p View Post
Does the rough idle change if you plug the brake booster line? If not, that's not your vacuum leak.
I will try this out. Either way I know the booster is bad, I have a stiff pedal that won't go away. I should be more specific too - the rough idle is a low frequency cabin shake that only happens when sitting in gear (R/D) with my foot on the brakes. If I'm in P, N, or driving - it's smooth.

Quote:
Originally Posted by 90xj06 View Post
iac does control the idle speed and if its all gummed and not working that could be a problem.
When you say speed are you talking RPMs? I idle very steady at ~700RPM and it barely budges. Still worth cleaning again like you say.
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Old December 8th, 2016, 08:31
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Re: Fast mechnical tick/whirl from intake manifold

its easy enough to do. just pop the 2 screws out and get a soft brissle brush. also take a look into the hole and see if its all yucky.
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Old December 8th, 2016, 08:56
RCP Phx RCP Phx is offline
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Re: Fast mechnical tick/whirl from intake manifold

It's on the other side of the motor, but the purge valve makes similar sound.
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  #11  
Old December 8th, 2016, 09:17
shmicah shmicah is offline
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Re: Fast mechnical tick/whirl from intake manifold

Quote:
Originally Posted by RCP Phx View Post
It's on the other side of the motor, but the purge valve makes similar sound.
Yup, heard that one yesterday. Similar "sound" but this one is MUCH faster (and fainter) than the purge valve.
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