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Random 'mini-revs' and noise from back of car? 

 

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 Post subject: Random 'mini-revs' and noise from back of car?
Posted: Wed Aug 14, 2013 11:36 pm 
Parts Gopher
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Age: 25

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Joined: 19th Feb 2013

Ride: NL Fairlane Ghia

Location: Sydney
NSW, Australia

Since I can remember, my car has always 'mini-revved' while in idling. I can hear the POD under the hood suck in air, and see my revs rise by about 50-100rpm? It isn't a lot, but it happens a fair bit (maybe once or twice every 10 minutes of idling.) Any idea what it could be and how I could fix it? The problem was still around when I was using the air box+panel filter.

The other issue is some noise from the back of the car when taking off from a stop. It's really hard to explain, but it sound like a small, quiet knock sound. This only happens when taking off from a standstill and doesn't seem to happen if I really baby the car off the line. Accelerating normally or heavily will make the sound, however. It also only happens after about 20-30 minutes of driving.

Car is a '97 EL Fairmont.

 

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 Post subject: Re: Random 'mini-revs' and noise from back of car?
Posted: Thu Aug 15, 2013 4:11 am 
Getting Side Ways
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Ride: 1992 EBII Fairmont

Location: Aga
VIC, Australia

If it's hunting at idle clean the throttle body and isc before replacing any ignition parts and check the manifold gaskets for vacuum leaks.

the knock could possibly be the diff or uni, put the handbrake on and the car in N and twist the tailshaft to check rear uni, axle raised and car in P to check front uni, if there's any play they're stuffed. This was mine and you can see the play is pretty bad.

http://www.youtube.com/watch?v=jIV23z43j7Q
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 Post subject: Re: Random 'mini-revs' and noise from back of car?
Posted: Fri Aug 16, 2013 2:23 am 
Getting Side Ways
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Ride: 5 speed XG ute

Location: Adelaide Hills
SA, Australia

That mini revving thing is exactly what my Nans old EL was doing when it needed new fuel filter. +1 for that sound being a uni...

 

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 Post subject: Re: Random 'mini-revs' and noise from back of car?
Posted: Sun Aug 25, 2013 5:27 pm 
Parts Gopher
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Ride: NL Fairlane Ghia

Location: Sydney
NSW, Australia

Just checked the tailshaft. Yeah, there's a little play there. Not heaps, but there shouldn't be any, so that needs doing.

Just installed a new fuel filter about 2 months ago and it didn't fix the hunting while in idle, so I'm now just assuming it's a vacuum leak. Any specific spots I should spray to find it? There's a hissing sound when idling that goes away under acceleration (my power steering high pressure line is leaking, I always assume it was that.)

 

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 Post subject: Re: Random 'mini-revs' and noise from back of car?
Posted: Sun Aug 25, 2013 6:19 pm 
Getting Side Ways
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Ride: 93 ED sedan

Power: 161 rwkw

Location: Rockhampton
QLD, Australia

xELFalconx wrote:
Just checked the tailshaft. Yeah, there's a little play there. Not heaps, but there shouldn't be any, so that needs doing.

Just installed a new fuel filter about 2 months ago and it didn't fix the hunting while in idle, so I'm now just assuming it's a vacuum leak. Any specific spots I should spray to find it? There's a hissing sound when idling that goes away under acceleration (my power steering high pressure line is leaking, I always assume it was that.)


Have you checked the intake manifold gasket ????

 

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 Post subject: Re: Random 'mini-revs' and noise from back of car?
Posted: Thu Aug 29, 2013 9:23 pm 
Getting Side Ways
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Ride: S1 eb 5speed

Location: Coffs Harbour
NSW, Australia

Mine has done this since I put in cam,chip and el ecu.
No vac leaks.
All sensors are spot on (as good as you'd get with a cam)
I can put it down to anything other then a ecu hiccup.
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