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You're right, the sensor is only in the loop when (archive)
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Posted by Bill B. on October 15, 2001 at 08:17:37:

In Reply to: O2 sensor really the culprit? posted by Sjef on October 15, 2001 at 08:01:29:


I thought that the O2 sensor would only work when the car and sensor have reached nominal operating temperature. So how could a faulty O2 sensor cause cold hard starting and rough cold idle? By the way, I experience this problem (hard starting, stalling, smelly clouds of raw fuel) about once a month, changed the coils and spark plugs but it didn't solve the problem.

Sjef
1990 520iM/M50
Netherlands

the engine coolant temp says it's ready to start sampling. However, I think the engine might have been running rich for a while (checking fuel mileage, I had been noticing a steady decline in mpg), and it finally sooted it up enough. I think the rough cold start and sensor failure were coincidental, but I think the sooting due to rich running sent it over the edge. Since then, I have not had rough cold start at all, and plugs are nice and light brown, not sooty like they had been.

Bill B.
'95 525ia


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