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Old 09-11-2010, 06:20 PM   #1
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Freaked out due to IMS reports - Newly discovered engine noise

Hey all,

I consider myself to be a good diagnoser of car noises. I know how to isolate, replicate, and eliminate.

On Friday, I was driving home from work with the top up. Now, in 2 months of ownership I pretty much have not driven with the top up. It's either down, or garaged. So bear that in mind. I've also de-snorkeled the car.

Driving home, I was in 5th gear around 2800-3000 rpms. I started to notice an engine noise similar to what I'd call road noise from worn out/scalloped tires...or a warbling bearing.

I let off the gas, it dissapears. I go down to 2500 rpms and push on the gas, and it doesn't appear again until 2800 rpms.

I move my head around the cabin, and it appears to be coming from the centerline of the car, behind the cabin.

I try to replicate this sound in 1st, 2nd, 3rd, and 4th gear. It only appeared in 4th gear, and then it was more slight than in 5th gear.

So, to re-hash, I've got a semi high pitched warbling sound coming from behind the drivers cabin centerline of the car. It only appears in 4th and 5th gears when the engine is loaded (I.e. gas pedal is being pushed) and appears around 2800-3500 rpms....

It doesn't appear in other gears, it doesn't appear when the engine is revved idling.

I am certain I have a bad front engine mount and I have de-snorkeled the car, which I know creates some very nice intake sounds around 2800 rpms....but I know those sounds, and I hear them in every gear. This is distinctly seperate.

Any thoughts on what this could be? '99 Boxster, 57.5k miles, car runs great.

Joe

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Old 09-12-2010, 04:55 AM   #2
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The first move is to replace the bad mount, when my car had a bad front mount, it allowed the engine to move far enough to make some previously unknown sounds. If your symptoms increase on downhills then it might be the mount. IMS= always spinning when the car is running so it should always make the noise.
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Old 09-12-2010, 05:34 AM   #3
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I suggest the following, in order:

1) drain oil, cut open filter element and inspect -- any metal flakes, even the tiniest of silver bits or plastic bits would be a strong indicator of a failing ims. If you see any, don't run the engine any more and proceed to installing the ln ims kit. Otherwise things are likely good good, refill with oil and enjoy.

2) replace front mount. This can absolutely cause unusual noises to be transmitted to the cabin as the engine moves around and if well worn the mount can allow metal to metal contact at certain revs.

There are other items that can produce troubling noises... cv joints, tranny gears, final differential bearings, pilot bearing for the tranny input shaft (but that is usually only heard with clutch depressed), and more... So don't immediately assume ims.

Good luck and report your findings.
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Old 09-12-2010, 06:19 AM   #4
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Another possible way to correlate your noise to the bad engine mount......when I bought Pedro's Enthusiast's Mount which is stiffer than the original, the vibrations I noticed transmitted to the butt sensor after the install occurred between 2800 and 3200 rpm's. Per other comments this is not unusual, which tells me this is a natural rev range to transmit vibrations.
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Old 09-12-2010, 06:39 AM   #5
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As others have said...

... first replace the front engine mount.
You may be somewhat used to the sounds a front mount make as it starts to crack, but as it worsens with time it starts generating new noises, especially if the center core wears down to bare metal.
Your CVJs will also add to the noise as more tension is applied to one side.
Don't wait any longer. You can do expensive damage if the engine mount is left damaged.
Happy Boxstering,
Pedro

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