Re: erratic idle - maybe O2 sensor or AIC - Saab 900 Bulletin Board - Saabnet.com
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Re: erratic idle - maybe O2 sensor or AIC
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Posted by JohnK (more from JohnK) on Fri, 5 Mar 2004 09:51:50 Share Post by Email
In Reply to: erratic idle, '88 900s owner, Wed, 3 Mar 2004 19:12:08
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A bad AMM will most often produce wide idle swings and stalling at cold start up. The idle then settles down as the O2 sensor warms up and starts to work.

The first component I would suspect is a bad O2 sensor.

If you connect a digital voltmeter between ground and the plug for the O2 sensor wire(don't unplug sensor), you should see the voltage fluctuate between 0.1 and 1.0 volts, 1/2 of the time above 0.5 and 1/2 below 0.5 volts. If the voltage doesn't vary or is skewed, suspect the sensor.

The next component I would suspect is the AIC. Give it a whack with a screwdriver and see if the idle settles down. Actually, I'd do this before you hook up the meter to the O2 sensor, since it only takes a second.

Then, clean the AIC with carb spray and finish with WD40. If it's stuck, you might need a new one.

You also could have a bad NTC temp sensor(under intake runners on head), I forget the resistance specs, but resistance goes down as temp goes up. I think if you search on NTC, somewhere in the hundreds of matches will be the resistnace specs.

Bad AMM's will also produce surging and flatspots under acceleration when warm.

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