perrys4

I read on a past thread that the idle is computer controlled and gets the needed info from a multitude of areas, one being the O2 sensor. Could a bad O2 sensor alone account for a slightly slow idle? I sense it may be bad because of barely passing NOX on my last test. I realize it could be MAF or other things but I thought I would start with O2 if it is related. Thanks in advance

Rich9928p

The best way to check if your O2 sensor is working is to do an exhaust CO test. On the newer 928s you need to pull the plug that is just before the catalytic converter to gain access to the "pre-treated" exhaust. Most shops have a CO tester.

Replacing the sensor yourself would probably cost about as much as a shop's labor to test it! So replace it and see if it makes a difference.

The idle speed regulator is controlled by the LH. You don't say if your's is an A/T or not. If it is an A/T you should see the idle speed drop a little when you put it in a drive gear. The idle speed should stay stable when the A/C is turned on.

John Speake

A slow idle means the loop is not in control and is out of range. When the loop is working correctly, idle speed should be steady under all conditions, except the idle speed drop when engaging "D" that Rich mentions.

A failed O2 sensor usually results in a very rich mixture. Bear in mind that the O2 loop is a closed loop system as well, and interacts with the idle system.