rattle at idle, goes away with rpm increase

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Hello All,

My Saturn sl1 1999, with 130k miles has developed a intermittent rattle at idle. The rattle goes away with ANY rpm increase at all, so far I have changed the Motor mount as these are known for failing(and mine was way past gone) this solved the noise for about 2 days(and made a huge difference as far as my car shaking), but now its back. It only happens at idle, if I give it any gas it goes away. to describe the noise it almost sounds like my car has a diesel engine, This doesn't happen all the time, and the noise is coming from the front passenger side of the vehicle, the car also has a slightly uneven idle(but not a full misfire), which I am hoping OEM spark plugs with fix, currently I have autolites that have been nothing but trouble.

Please let me know your thoughts, my current thought is a Timing Chain or tensioner which I am really hoping it is not (I am OCD about the oil level in the car), I have also read these should make noise through out the RPM range and not at idle..

Any and all help is welcome.

Thanks!
 
Is the car a 5 speed manual?

If it is, try putting your foot on the clutch while it is at idle or have someone else do it while you stand in front of the car and listen. A clutch release bearing is capable of making the sound you describe. There is usually no reason to worry, but that could explain your noise.
 
Not sure oil level matters on chain, as much as good oil does--I'd think low oil level would be bad overall.

Not a heat shield on the exhaust?

Noises sometimes are odd, they don't always come where you'd expect. If it occurs only at idle I'd walk around the car and see if you can find it.
 
it is a five speed manual, I don't believe the sound to be coming from the transmission, (although my transmission does have a slight clatter which i have read is normal for manual transmissions).

Also there is no heat shield on the exhaust manifold, but I am not sure about under the car.

I am kinda hoping it is just a loose part or something somewhere, because the noise just kinda appeared out of the blue, it is a consistent noise when its there, never louder or quieter.
 
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Originally Posted By: nitehawk55
Exhaust manifold leak ?



Hmm, I have not even considered this, but wouldn't this happen constantly? and not intermittently?
 
Originally Posted By: nitehawk55
Exhaust manifold leak ?


More likely a heat shield on the exhaust is rattling on the exhaust pipe or cat converter. I have the same on my Audi as the heat shield on the converter is held on with bolts on the top and just a worm clamp on the bottom, and the worm clamp doesn't survive that well. I have to change out the clamp every year or so.
 
Hmm, would this be the heat shield underneath the car? above the cat converter?

If so would this be visually loose? or would i need to start the car and get under it and watch/listen?
 
Check the muffler strap. They are known to become weak and causes the exhaust system to rattle. Check the heat shields while you're under there.
 
Best way to pinpoint noise is if you have a piece of garden hose 2-3 feet long and put one end to your ear and the other around the area you think the noise is coming from .

I said exhaust manifold as the noise will usually be more noticeable when it is first started or it could be where the exhaust pipe is bolted to the manifold and that could be more constant but the pipe may move and seal the small leak .
 
Originally Posted By: GSCJR
Check the muffler strap. They are known to become weak and causes the exhaust system to rattle. Check the heat shields while you're under there.


My muffler strap is currently broke (and on my list of to-dos), but I have checked this, it only makes a sound over bumps, a loud clunking.. I will check to make sure nothing new has happened and is causing it to rattle, but the sound definitely appears to be coming from the front end of the car, I could see it being something rattling up further in the exhaust system thought which I will look into.
 
Has the idle speed itself changed, or are you just hearing a new noise?

On my '94, I started to notice a more pronounced rattling and buzzing of the various broken interior pieces. I tracked that down to a slightly lower idle speed, brought on by the EGR valve sticking open. (That's what I got for cleaning out a totally plugged EGR passage.)
 
the idle is still about where it has always been right about the 800 rpm mark
i think standard idle for this car is about that.. somewhere between 800-850ish. So this is a new noise.. The car burns about 1.5-2 quarts of oil between 3000 ocis I imagine this could coke up the EGR valve pretty well. I have never inspected the EGR, and have never gotten a check engine light, I may pull it off and inspect and it could be the cause of the slightly uneven idle.

Edit, I will mention that EVER SO SLIGHTY the rpm needle has bounced, and you really have to watch it to notice.. but this is nothing new either.
 
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I'm confused. Your OP says at idle? Over bumps? Your control arm bushings are worn out then.
 
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Originally Posted By: GSCJR

I'm confused. Your OP says at idle? Over bumps? Your control arm bushings are worn out then.


Sorry I don't mean to confuse, this is strictly an idle issue. the question was asked about my Muffler strap being broke and causing the sound. My muffler strap is in fact broke and has been for some time, but doesn't cause a idle noise, only a noise over bumps. The issue at hand is still a idle rattling sound, just trying to get ideas where it may come from.
 
Originally Posted By: zzyzzx
I think you should check the exhaust heat shields. You might have missed something there.


Hi,

I will check underneath the car and report back to see if i can find anything loose.

Thanks!
 
What is making me feel better as no one seems to think its engine/timing chain related issue.. or at least no ones mentioned that yet.. Does this not fit the symptoms of a mechanical engine issue since its going away with any amount of throttle being applied? I could fix most things i put my mind into.. but really don't want to tear into my engine.

Thanks.
 
Originally Posted By: actionstan
What is making me feel better as no one seems to think its engine/timing chain related issue.. or at least no ones mentioned that yet.. Does this not fit the symptoms of a mechanical engine issue since its going away with any amount of throttle being applied? I could fix most things i put my mind into.. but really don't want to tear into my engine.

Thanks.


Use the hose (stethoscope) as I suggested , it will help you pinpoint noises if you can't find them otherwise .
 
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Your rattle question reminds me of the neighbor kids first car, beat up 70s Datsun wagon. Saw him often nosing around under the hood presumably checking oil, water, etc. A couple of months later he ask me to see why it was making a rattling sound at idle but went away when the rpms went up. After spending an hour or more checking for loose/broken parts, ignition timing and even removing the accessory belt, it still rattled and I was getting stumped. Finally I jokingly ask him about the oil level. His answer was "How do you check it?" I first thought he was pulling my leg but soon realized he really didnt know!
Pulled out the dipstick and it was bone dry. Added 2 quarts before it showed on the bottom end and another 2 to reach full. That thing was running on less than 1/2 quart of oil. It idled perfectly normal with more oil in it. One tough little 4 banger. Amazingly he drove that car for another 2-3 years without any other problems, but he did learn how to add oil.

My lesson learned was never assume anything and start with the most basic trouble shooting.
 
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