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Discussion Starter #1
Hi again,
today i cleared 2 codes from my m5 that facing rough idle and stalls.

oxygen sensor and air intake temp sensor.

Are those 2 sensor make the car stall with rpm going under 400.

Is there a numbers in ohms for both sensor to test with ohmmeter.

i used carsoft scanner.
temp sensor -49 degree 2000ohms.
timing shows -2 and -6 when the car stalls..

please advice .
i am sure that i have air leak .
i will do smoke test as well.

thank you
 

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The air intake sensor is on the air filter box. It is a set-point for the DME to adapt fuel enrichment just like a choke during cold intake air..
Hence, if the air temp sensor reads -49 deg.C = -56 deg.F the DME will be on full enrichment for very cold intake air and the engine will have trouble idling in warmer air temps due to the extra rich fuel mixture.
A -49 deg.C reading would indicate a open in the temp sensor circuit.
However, 2k ohms should indicate a temperature reading above +20 deg.C = +64 deg.F.
The coolant temperature sensor has the same effect on fuel enrichement and the coolant sensor for the DME produces the same ohms value for temperature measurement.

The O2 sensor is part of the fuel injection closed loop system and an O2 fault code will cause the DME to default to a nominal .5V, O2 sensor reading, which should cause a stoichiometric air fuel ratio. If the O2 sensor is the only defective component the engine will typically idle normally.
An intake leak will often cause the DME to enrich the air fuel mixture to compensate for the faults air leak and that can cause an O2 sensor adaption fault but it has nothing to do with the -49 deg intake air temp reading, that will cause an enrichment adaption that can cause an O2 sensor fault also.

I would attend to the intake air temp sensor measurement -49 deg C. error first: 1) make sure the connector is plugged-in, 2) test air temp sensor for the correct temperature reading, 3) make sure the diagnostic software is correctly reading the intake air temperature; as this is a primary DME set-point that must function correctly before other systems in the DME can function normally.

Also, check the fuel rail pressure and make sure the fuel pressure regulator functions correctly as a low/high fuel pressure will cause havoc for the idle air fuel ratio to include rough idle, stalling, O2 sensor adaption fault, etc. but the Fuel Pressure is a fuel injection open loop value and there is no way for the DME can produce a low or high fuel pressure fault code.
 

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Discussion Starter #3
Thank you for the quick reply.
I tested the connector to iats
i found 1 pin with 4.9 volts and the other is null should it be connected to tge ground?
correct me if im wrong.

i assume without groud the dme will not see the sensor and will read -49

2k ohm around 20 degrees is the real air temp now and this means the sensor is not faulty.
 

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Pin 2 of the temp sensor needs to be connected to chassis ground. With the sensor unplugged, use an ohm meter to measure the zero ohms from pin 2 on the connector to a point on the chassis, engine metal will work.
Be aware the M5 has aging electrical systems that could display intermittent failures (wire insulation, connector crimps, connector contacts and electrical components) that seem good when you test the circuit but are still the cause of a system failure .
Before I would say any sensor is good, I would either know I found the problem and the sensor was not it or replaced the sensor with a known good component and the failure still exists.
Some times replacing electrical parts is a good thing because that helps put some youth back into the electrical systems and also provides spares to help with troubleshooting.
Old cars are not always inexpensive even when they are cheap to buy.
 

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Discussion Starter #5
Found it brown orange wire is cut from the plug.
now i will chase the air leak.

thank you
 
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