1984 944 Heavy vibration at idle

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Jake77 - 05 Feb 2009 11:58 GMT

Hi all:

My 1984 944 has had a heavy vibration at idle since purchasing it a
year and a half ago. Everything runs well(very well in fact) and I
have mainly made cosmetics repairs other than an alternator
replacement.The vibration seems to be coming from the engine
compartment, and is strong enough that when idling the front end
visibly vibrates. Upon accelleration, even at speeds as low as a few
miles an hour, it seems to almost or completely disappear, only to
return when after stopping again.

My friend who is more mechanical than I am said that he thought
vacuum leak somewhere could be the culprit, while I suspected motor
mounts.

Has anyone else had this problem, or know if this is typical for that
year and model? (It's a non-turbo, auto transmission version, by the
way.)

Thanks

David

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Jack D. Russell, Sr. - 05 Feb 2009 12:49 GMT

Jake77 <mcwilliams@mindspring.com> wrote in
news:ca6778fe-070d-4b01-9818-9ca4dd2f5ed3@b16g2000yqb.googlegroups.
com:

> Hi all:
>
[quoted text clipped - 18 lines]
>
> David

Typical and your guess is probably correct. 99% of the time,
vibration at idle only,with the 944, is indicative of bad motor
mounts. Do yourself a favor and replace them with the genuine Porsche
mounts, if you don't want to do them again in a year or two.
See:
http://www.clarks-garage.com/shop-manual/eng-11.htm
http://www.clarks-garage.com/shop-manual/eng-12.htm

Good luck.

Signature

Jack

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Bill Noble - 06 Feb 2009 05:50 GMT

here is what to check, and the order in which to check them:

1. check that the balance shafts are properly timed - if one or both are off
by a few cogs, it really messes up smoothness at idle and would match your
symptoms - I had this happen on a recently purchased car, since the belt was
good and they were "close" I didn't catch it until time to change belts.

2. check distributor cap - junk inside/bad cap will cause trouble and make
idle rough, so will bad plug wires, but less so.

3. check motor mounts - the one on right side fails first - compare
thickness on the two sides, a collapsed mount is pretty obvious.

4. the 944 is quite succetptible to vac leaks, check the J-tube for cracks,
particularly where other tubes join it.

5. bad air flow meter will do this, and they tend to wear most near the idle
position.

> Hi all:
>
[quoted text clipped - 18 lines]
>
> David

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