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Re: Idle fluctuates with o2 signal Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Fri, 16 Feb 2007 12:05:01 In Reply to: Idle fluctuates with o2 signal, grlyd, Thu, 15 Feb 2007 21:36:51 Members do not see ads below this line. - Help Keep This Site Online - Signup |
It could be the O2 sensor, but likely not. If the idle were erratic for other reasons, as it fluctuated the mixture would also. So the O2 sensor is probably just reporting the truth, not causing the problem.
When the engine is cold, the O2 sensor isn't in the picture, and the ECU sets the mixture a little rich. When the car warms up, the ECU leans out the mixture, and usually the idle drops a little. The erratic idle could be a few things. It could be a stick AIC that just needs to work a bit before it works well. It over-and under-shoots, causing the loping idle. The ECU may be cutting back the mixture too soon, while the sides of the throttle body are still cold; the injected fuel condenses on the side of the body, and the warm idle circuit isn't working quite right until things warm up.
Quite frankly, the warming-up idle on the 900 has never been stellar. If the problem is really annoying, I'd be looking for vacuum leaks. It might be something weird like a slightly loose clamp on an intake plenum hose (there are four), that allows a slight vacuum leak until things warm up, expand, and seal the leak. When cold, the extra enrichment covers up the issue.
posted by 192.249....
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