Rough idle on early 1985 944

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Ian - 13 Apr 2006 20:02 GMT

I own an early 1985 944, and it has a rough idle. When I first start
the car, there's a loud shaking and/or rumbling sound coming from
underneath the car. When I accelerate at or over 1500 RPMs, the
shaking and rumbling goes away, but then comes back once the RPM
falls back down. It seems worse in cold weather. After about 15
minutes of driving or just warming up, it seems to smooth out. I have
replaced the oxygen sensor and spark plugs, but that did not help
any. This 944 has an automatic transmission.

Any pointers where to start looking?

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Ian

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darthpup - 13 Apr 2006 23:12 GMT

You need to go over the entire vacuum system and look for cracked or
broken connections.
Also, the o rings around the injectors are probably dried out and
leaking air into manifold. There must be an o ring on the oil filler
cap or the vacuum system will be compromised. Spray some gum out into
the sliding air flow valve with the rubber boot pulled back. All these
items will help with rough idle.
Since the problem disappears after warm up it could be the temperature
sensor is bad and or the aux air valve. Check www.clarks-garage.com
also.

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PDX944 - 14 Apr 2006 00:48 GMT

Try new engine mounts.

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Fred Aston - 14 Apr 2006 18:45 GMT

My '89 did the same thing. I sprayed WD-40 around the intake manifold where
it meets the block. When the spray hit right spot, it momentarily smoothed
out. That indicate exactly where my air leak was. I replaced the gaskets
and it runs beautifully.

>I own an early 1985 944, and it has a rough idle. When I first start
> the car, there's a loud shaking and/or rumbling sound coming from
[quoted text clipped - 6 lines]
>
> Any pointers where to start looking?

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joliett - 15 Apr 2006 06:24 GMT

MOTOR MOUNTS

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joliett

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