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Question Odd co2 readings...

Ok, my car started crazy surging at idle a few weeks ago out of the blue. So, I posted a topic on the subject and good 'ol JW came to the rescue telling me it sounded like the idle mixture was too rich. I borrowed Pat S's co2 tester and indeed I was running at about 9 (specs call for anywhere between .5 and 1.5) So I adjusted my idle mixture and went ahead and ordered a o2 sensor since mine was disconnected. Since then my gas mileage has gone up about 3 mpg and she runs great...well almost.

I've noticed that when adjusting my mixture, the co2 would range from .5 then run up to 1.5 then back down to .5 again. This went on for as long as I was monitoring my emissions. I also noticed that at idle, my idle will SLIGHTLY surge between about 800-900 rpms. The slight surging I've noticed is with the o2 sensor engaged and I dont believe I've ever noticed it before. Does anybody have any ideas on this one? She seems to run fine, but the small amount of surging and the mixture fluctuation concerns me.

Any ideas?

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'82 911SC Targa!
Old 02-23-2005, 08:00 PM
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CO....right?

Not CO2......

big time difference......

????

Wil
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Old 02-24-2005, 06:27 AM
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the surging is the oxygen sensor adjusting the mix. you can also feel the slight surge when cruising. i don't care for it much, and normally leave the sensor unplugged. if you set the CO to 3-3.5%, it will idle smoother. did you happen to check to see if the relay for the O2 sensor system was working? it's under the right seat, in front, by the tunnel. get the engine hot, then unplug it for a moment. the engine should run noticably rougher if it was working. the rest of the O2 sensor system has to be functioning, even if the O2 sensor is left unplugged.
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Last edited by john walker's workshop; 02-24-2005 at 06:58 AM..
Old 02-24-2005, 06:52 AM
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Don't forget to look for vacuum leaks or the notorious intake leaks, the will screw up your mixture also. Use the carb cleaner and spray around, increase in idle, you have a vacuum leak. Don't spray near air filter, as you would expect, idle will go up then.
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Old 02-24-2005, 08:30 AM
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I'll check the mixture again tonight, but with CO being around 4-5, it surges wildly at idle. Time for another mixture adjustment

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Old 02-24-2005, 09:01 AM
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