91 Golf wet exhaust valve, rough idle in winter

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MasterChifa@gmail.com - 13 Nov 2008 23:04 GMT

Hi All,
Thanks a lot for helping me out when I installed my new dual downpipe
exhaust. She sounds fantastic now. Far better than the previous rattle
+ leak combo. And thanks again for helping me out with her second
exhaust leak. It turned out to be an install error on my part. I put
the exhaust manifold gaskets all on in the same orientation, the two
on the left are supposed to be opposite the two on the right. (On the
brighter side, I'm getting good at taking the manifolds off!)

While I had the manifolds off, I checked out the valves. Three of the
exhaust valves looked gray and dull while the last was black and
glistening (looked wet to me). What might cause this? and is it
something I need to be concerned about? I plan on keeping the car for
~two more years.

Also, we're approaching winter and every year when the temperature
gets low like this her idle starts getting unstable on a cold start
and improves (although not great) once she's warmed up. It'll hang
around 900-1000 rpms then slowly drop to almost stall (200?) then
jumps back up, or she just stalls. I read that vacuum lines can affect
this, having just removed the intake twice, I know the vacuum lines
are in good shape. The only questionable one is on the rear side of
the intake. It also sounds like the idle stabilizer valve could be an
issue, how can I test this?

This almost stall situation can be replicated. If I rev the engine up

>2000 or so, the idle will catch at 800-900 like it's supposed to.

However, If I give her a slight bump then take my foot off the gas,
the idle won't catch and she may stall.

thanks,
Matt

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dave AKA vwdoc1 - 14 Nov 2008 02:08 GMT

> Hi All,
> Thanks a lot for helping me out when I installed my new dual downpipe
[quoted text clipped - 4 lines]
> on the left are supposed to be opposite the two on the right. (On the
> brighter side, I'm getting good at taking the manifolds off!)

congrats to you!

> While I had the manifolds off, I checked out the valves. Three of the
> exhaust valves looked gray and dull while the last was black and
> glistening (looked wet to me). What might cause this? and is it
> something I need to be concerned about? I plan on keeping the car for
> ~two more years.

maybe a leaking injector or bad valve guide seals?
Or even a bad/leaking fuel pressure regulator.

> Also, we're approaching winter and every year when the temperature
> gets low like this her idle starts getting unstable on a cold start
[quoted text clipped - 5 lines]
> the intake. It also sounds like the idle stabilizer valve could be an
> issue, how can I test this?

The Bentley Repair/Service manual will give you the proper procedure for
setting up the ignition timing and adjusting the idle speed along with
checking the Knock Sensor.
The ground wires attached near the rear of the valve cover or by the
cylinder head coolant pipe usually try to break off causing nasty running
problems.
Also check the wires to both switches on the throttle body.

> This almost stall situation can be replicated. If I rev the engine up
>>2000 or so, the idle will catch at 800-900 like it's supposed to.
> However, If I give her a slight bump then take my foot off the gas,
> the idle won't catch and she may stall.

Ign timing, basic idle speed should stop that hopefully. A clean Idle
Stabilizer Valve should help too, but some vehicles can run without a
functioning one. ;-)

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later,
(One out of many daves)

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