Quad 4 Closed Loop Question

My car generally runs good. A problem is that sometimes, about a minute after a cold start, it will stumble for a few seconds. Usually I'll be in a parking lot or in the driveway so it is not much of an issue. Last week it happened after I pulled into traffic.

A scan tool shows that it goes into closed loop about a minute after a cold start (40 deg F.). It cycles back to open loop then closed several times before it stays closed. This happened before the O2 sensor reached .5 volts. I think that this might be a clue to the problem. Once running hot, the O2 sensor will cycle from rich to lean several times a second.

My question is what allows the engine to go into closed loop?

Thanks

Reply to
Scott Buchanan
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Reply to
Shep

Any codes showing up? As was mentioned check the coolant sensor. It can be monitored on the OBDII tester.

Reply to
Woody
1995 Grand AM. It is not a heated sensor. I think that the coolant temp was not more than 80 deg. F since it had been running less than a minute before going into closed loop. I'll check tomorrow. As mentioned, the O2 voltage had not reached .5 volt so it should not have been hot enough to work yet. This is assuming that open loop is running rich and not lean not allowing it to reach .5 volts.

What should the coolant temperature be?

Reply to
Scott Buchanan

No codes.

Reply to
Scott Buchanan

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Reply to
Shep

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