O2 disconnect
06-19-2011, 11:17 PM
#16
Rennlist Member
Thread Starter
06-20-2011, 03:39 AM
#17
Racer
Malcolm,
if you use the diagnostic tester on the diag bus, you will first of all see if the idle contact is actually seen by the LH and if it works at all times. There is another neat feature on the LH tests of the tool showing the actual sensor values. It shows you if the O2 sensor actually works. It is far from perfect, but if it is unable to show a working sensor, you have either a LH failure, or a bad sensor (maybe even a disconnected wire, or the internal 12v supplied heater does not work).
If you want to go into "what is the sensor doing during driving", you need different tools. I made my own monitoring tool but Lambda display gauges aren't that hard to get. Consider a wideband setup.
Will a bad O2 sensor affect idle? Yes. A rich or lean fuel level will not be compensated and will create stalling or rough idle.
1400 rpm at startup is high, sounds like an intake air leak somewhere or a bad MAF. Disconnect the 12v and see if it is back to 1000 at first few seconds, and drops to 675 (750 manual) after 30 seconds. If it gradually climbs up to 1000 rpm again you have a leak somewhere and unmetered air is entering the system, or the MAF is sending wrong information.
Like John already said: if the LH does not detect a working O2 sensor it stays in open loop mode and uses a coarse fuel mixture adjust based on rpm.
Oh, removing the O2 sensor? No big deal is it breaks loose. But it can be a bitch and lots of heat may be required. You already mentioned the diverter pipe. Same problem.
regards
Theo
if you use the diagnostic tester on the diag bus, you will first of all see if the idle contact is actually seen by the LH and if it works at all times. There is another neat feature on the LH tests of the tool showing the actual sensor values. It shows you if the O2 sensor actually works. It is far from perfect, but if it is unable to show a working sensor, you have either a LH failure, or a bad sensor (maybe even a disconnected wire, or the internal 12v supplied heater does not work).
If you want to go into "what is the sensor doing during driving", you need different tools. I made my own monitoring tool but Lambda display gauges aren't that hard to get. Consider a wideband setup.
Will a bad O2 sensor affect idle? Yes. A rich or lean fuel level will not be compensated and will create stalling or rough idle.
1400 rpm at startup is high, sounds like an intake air leak somewhere or a bad MAF. Disconnect the 12v and see if it is back to 1000 at first few seconds, and drops to 675 (750 manual) after 30 seconds. If it gradually climbs up to 1000 rpm again you have a leak somewhere and unmetered air is entering the system, or the MAF is sending wrong information.
Like John already said: if the LH does not detect a working O2 sensor it stays in open loop mode and uses a coarse fuel mixture adjust based on rpm.
Oh, removing the O2 sensor? No big deal is it breaks loose. But it can be a bitch and lots of heat may be required. You already mentioned the diverter pipe. Same problem.
regards
Theo
06-20-2011, 08:16 AM
#18
Rennlist Member
Thread Starter
excellent Theo.....I will use the PDT999 on the car but thats a seperate discussion (this is the 87 S4 we've chatted about).
I have the batt disconnected and shall tshoot again once I swap out the O2 sensor and remove the inspection cover for the 'other' work
The biggest issue with the idle is the surging and stalling......I am of the mind set that the intake has to be refreshed but want to explore all possibilities.
I have the batt disconnected and shall tshoot again once I swap out the O2 sensor and remove the inspection cover for the 'other' work
The biggest issue with the idle is the surging and stalling......I am of the mind set that the intake has to be refreshed but want to explore all possibilities.
06-25-2011, 01:12 AM
#19
Rennlist Member
Thread Starter
To complete the thread:
exhaust system dropped, OEM O2 sensor removed and replaced, removed the inspection cover and pipes back on.
The batt was disconnected so the ecus reset.
Car started at +1400 rpm and after a few mins fell to normal idle until it was fully warmed then the idle stumbled slightly. Short drive to get everything fully to temp and the bad idle miss was there....conclusion, it wasn't the O2 sensor causing the issue.
Off comes the intake
exhaust system dropped, OEM O2 sensor removed and replaced, removed the inspection cover and pipes back on.
The batt was disconnected so the ecus reset.
Car started at +1400 rpm and after a few mins fell to normal idle until it was fully warmed then the idle stumbled slightly. Short drive to get everything fully to temp and the bad idle miss was there....conclusion, it wasn't the O2 sensor causing the issue.
Off comes the intake
Last edited by the flyin' scotsman; 06-25-2011 at 08:02 AM.
