Thread: What is this?

The O2 has 2 parts one part heats it up the other part is the sensor. The heater part can go bad while the sensor can be good. So that is one way the O2 can be bad and the ecu wouldn't know. If the heater was bad you would have bad idle until the motor was driven and warmed up. Keep that in mind when you do the unplug test on the o2

The car does not have a bad idle, the only issue with the car is bad hesitation between 2k-3k rpms.

Ok then you have it easy if you want to test the O2. Just let the car warm up ten minutes before you do the unplug test.

Have you checked your distributor cap and rotor? Could be vacuum leaks too

No vacuum leaks, it has a new cap and rotor.

Usually a cap like that either fuel vapors, or air compressor refrigerant running through that line.

MAF is entirely possible.

If you had a vacuum leak, you'd probably notice it, ie idle is *too high* ( intake side ) or car struggles to idle ( valve cover gasket, leaking PCV hose, etc ).

That specific cap thing was a part of the fuel vapor exhaust outlet as was on my 01' RR sentra. Except the location seems to be different.

Ok, I unpluged the O2 sensor when the car was warm. There was NO difference at all and I did not get a CEL or an error code. Is this normal? It was unpluged for at least 2 minutes. Or do I have to drive the car to get an error code?

No vacuum leaks, cap and rotor are new.

Try driving around the block or a short distance and see if there is a difference in how the car drives. I would be looking around for a new O2

Some times it takes the ECU a little while to through a code when a sensor is bad

I will try that, I let you know. Thanks

BTW i just cleaned my MAF. It was effing horrible. No wonder the car was dying at idle randomly. I had a problem at a certain RPM range also.

Worth a try.