Re: Unsteady idling - Saab 9000 Bulletin Board - Saabnet.com
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Re: Unsteady idling
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Posted by David Ingram (more from David Ingram) on Mon, 11 Dec 2006 12:41:37 Share Post by Email
In Reply to: Unsteady idling, Oni, Sun, 10 Dec 2006 08:51:34
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Hi Oni!

Glad to hear the beast is still running!

First thing to check anytime you suspect head gasket (or head bolt torque) issues is the presence of inordinately steamy exhaust, which would indicate coolant being burned up in the combustion process. Given the newness of that gasket, I'd have my doubts that such a situation applies. And at this time of year, you can't really gauge steamy exhaust since it's cold out anyway.

More likely, the wetness and gunkiness of your plugs emanates from a too-rich fuel mixture, which will leave behind carbonaceous goop because it's incompletely burned fuel.

Given that your idle seems to steady itself after it's warmed up, I suspect your O2 sensor is getting old. If it's giving faulty readings as to the amount of O2 in the exhaust, it'll prompt the engine to enrich and lean out the fuel ratio, alternating back and forth until it finds its equilibrium. When the car's cold, this condition is especially noticeable as the car's brain works extra hard to prevent emissions until the catalytic converter reaches its operating temperature.

Once you warm up, the problem appears to go away but is still probably averaging the mixture on the rich side of the spectrum, giving you gunky and wet plugs. Have you noticed a decline in fuel economy lately (not a guarantee that you would but people often do in these circumstances)?

There may be some means to test the O2 sensor, say by disconnecting it to see if the idle stabilizes, but I don't know having never personally had O2 sensor issues.

posted by 155.212.49...

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