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HUNTING IDLE, O2 Sensor related 700

posted by  Brick Skinner on  Thu Jul 23 14:55 CST 2009
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last visit: Fri Jun 13 13:31 CST 2014
[RELATED]

I've had this small nagging idle hunt for some time now. Between, say, 600-900 rpm. Over the months I have eliminated all possible causes except one; the O2 sensor. I replaced the head gasket a few months back because it was in real bad shape and leaking into the cylinders. I figured I was immune to the possibility of silicone contamination to the sensor so I didn't think it was a concern.

Well I stuck an o-scope on it today and a few things came to light. The first thing is that I do have about a 0.1-1.2 volt pulse except that it is very slow, about once every 1 or 2 seconds. Also, it seems like the sensor heating circuit stays on at around 13.2vdc.
NOW, here's what I don't understand: when I disconnect the red and white (heater) wires, the idle surge goes away and the pulse flatlines at 0.0 volts and the engine runs smooth as silk. When the red/white pair is re-connected the pulse gradually widens, over a period of about 15 sec's, along with the idle surge.

Questions:
1. Should the pulse be much shorter?
2. When should the heater circuit turn off?






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