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I have changed the O2 sensor, the Aux Air Valve and the various temp sensors on the thermostat on my 1980 528i auto and still have a cold idle problem. Once the car warms up the idle is fine. As a test I disconnected the O2 sensor started the car cold, it started and idled fine. If I reconnect the O2 the RPMs drop and the idle becomes rough. Disconnect all is good. Would it damage the engine if I drive the car with the O2 sensor disconnected all the time? Any insight would be appreciated.

It could damage your cat and hurt your gas mileage. Along with generating more smog.

I've heard that sometimes you could buy a new 02 sensor that is faulty. Try taking it back, with the receipt of course. I don't know if there's a guarantee.

Thank you for your advice. I bought the Bosch OEM sensor a year ago. The car passed Cal smog test with flying colors two days ago with the O2 sensor hooked up. I am not driving the car with it dis-connected. I will take out my multi-meter this weekend and run some more tests.

pmaronoff wrote:Thank you for your advice. I bought the Bosch OEM sensor a year ago. The car passed Cal smog test with flying colors two days ago with the O2 sensor hooked up. I am not driving the car with it dis-connected. I will take out my multi-meter this weekend and run some more tests.

Keep us posted...this is interesting. I am not expert, but I am guessing that something other than the 02 sensor is wrong.

I agree. The O2 should not kick in until the engine is warmed up. I will post any results.