noturbo

I am the owner of a 1993 968 with a Tiptronic trans. While I was driving the car yesterday, I was stopped at traffic lite with the car in drive and at idle when I heard this sound from under the car.

When the car is in drive and at idle there is a noise or rattle which seems to be coming from the rear of the engine, can’t tell if it’s the left of right sides. It also occurs on start-up in park but only for a second or two.

The noise is more like a “dieseling” sound but goes away at approximately 1000-1500 RPM while in drive only. I don’t believe it’s a rod knock because it only occurs at low RPM while the car is in drive. The car or engine does not shake or any thing else, it’s just an annoying noise-any ideas on what this could be?

Any help in my quest to find the cause of this and suggestions on repair would be greatly appreciated.

Thanks,

RajDatta

It could be something as simple as loose or broken exhaust. I have seen instances were a part of the inner muffler loosens over time and causes this rattle. Its only present at certain rpm due to the resonance and goes away at higher rpm. I would check the rear muffler and the center resonator to make sure nothing is loose in there. It should be an easy test.
Try tapping the muffler and resonator with a screwdriver and see if you can hear the rattle.
Good luck.
Raj

Lord_Galva

Ah finally someone sharing my pain. I also believe its the exhaust pipe. Mine is doing the same after I hit a curb funny. Got under the car and found the break right after the cat. You can weld or (the better option) buy a new one. Unfortunatly I'm broke, so I'm keeping my fingers crossed that I don't need to pass smog to register my car this time around.

noturbo

It seems possible that the noise is from an exhaust leak but from my initial inspection the sound is coming from the rear of the engine compartment in the general area of behind the left wheel. My initial diagnosis is maybe a motor mount, does this sound reasonable?

On a related note, any takers on why a motor mount for a tiptronic trans is 5 times more expensive that for a manual? Anyone know a good source for a couple of mounts, should this prove to be the source of the noise?

RajDatta

It could possibly be a collapsed mount. The general feeling is that the tiptronic uses a much stronger mnotor mount and that is why it is much more $$. I would not cut corners, make sure you use the tiptronic mount. I have heard of people use a standard one and it failed.
Raj

RajDatta

It could possibly be a collapsed mount. The general feeling is that the tiptronic uses a much stronger motor mount and that is why it is much more $$. I would not cut corners, make sure you use the tiptronic mount. I have heard of people use a standard one and it failed.
Raj

austex

flex plate ?

RajDatta

Scott, that would be an excellent guess. They are known to fail after all. Hopefully Scott Harrison will chime in since he owns a tiptronic cab.
Regards.
Raj

noturbo

Coming from the 911 world I have to plead my ignorance, what is a flex plate? what does it do and how would I check to see if it has failed?

Thanks for all the info..

oppositelock

Flex plate is a rubber centered disc that connects the crankshaft to driveshaft. Also has starter ring gear on it. To check, be under the car and remove the large rubber plug in the bell housing above the starter. If rubber bits fall out, it has failed. Also shine a flashlight in there to check the condition of the flex plate. From your description, it sounds more like a cracked heat sheild or exhaust. There are many heat sheilds on these engines and even more on the tip cars. Flex plate failure makes a big scary noise.
Mitch

noturbo

Well the good news is I removed the plug above the starter and no rubber was to be found and upon further inspection the area inside the bell housing we clean and debris free. Does this eliminate the flex plate as my noise source?

The bad new is I still can't find the noise. It's difficult to be under the car while it's in gear. Because, it only occurs when in gear.

RajDatta

This one might require a volunteer then. Ideally, you can pinpoint the location and then figure out the cure. Make sure you use great precaution when getting under the car while its in gear, scary place to be.
Raj