Unofficialbmw.com

[lrayvick]

I need an opinion about the intake air temp sensor (MAF). Bentley says the resistance across the terminals should be 2.5 K ohms at about 70 degrees F. I checked them all and got between .5 and 1.6. Anyone know how to test these?

BMW calls them the Intake Air Temp sensor but most refer to them as the Mass Air Flow sensor. (IAT/MAF). I see prices ranging from $75 delivered used to about $300 new.

I am in So Cal. Failed smog inspection by max limits on CO2, fine on CO and NOX. New OEM spark plugs. 140 K mi on motor which runs great, doesn't use oil, etc. Cats check out good and Bosch O2 sensors were new 20 K miles ago.

Found it was throwing code 1213 - Lambda Control 2 which means lean or rich condition due to "fuel tank ran empty, incorrect fuel pressure, injector valve defective or coked, engine temp sensor defective, secondary air leak, fuel evaporation control system defective, air flow meter defective and/or the combustion is being disturbed by mechanical failure (spark plugs, compression, intake/exhaust valves, ...etc.)"

From the smog check it is running a little rich. Fuel tank did not run empty. Fuel pressure is in spec.
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1994 530i Auto

[lrayvick]

Also I unplugged the sensor and started the car. It seemed to run a little rough and the check engine light came on. Plugged the sensor back in with the motor running and it died. Restarted it - as before.
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1994 530i Auto

[edjack]

These are two different sensors. The temp sensor is in the air filter box. The MAF is in the intake plumbing downstream from the box.

Replace the temp sensor, and report your observations.
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Ed BMW CCA member since 1987 (Nr. 62319).
'97 540i 6 speed Aspensilber over Aubergine interior.

[lrayvick]

Edjack - thanks for the clarification. I was confusing the IAT and the MAF sensor. I just didn't read far enough in the manual and did not understand that the IAT sensor is in the intake manifold on the M60.

I read the resistance as 2.98 K ohms at 50 degrees F. One spec is 2.1 to 2.9 K ohms at 68 degrees F. So it looks to close enough.

I checked for secondary air leaks and the hoses on the fuel evap system and found no obvious issues. I do have a new aftermarket gas cap which seems to fit tight as a drum.

It looks like that leaves such things as an "injector valve defective or coked, air flow meter defective and/or the combustion is being disturbed by mechanical failure (compression, intake/exhaust valves, ...etc.)"

I guess I could take a chance and buy a used MAF. I see OEM ones for about $70 delivered and guaranteed for 30 days. That might eliminate one more variable.
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1994 530i Auto

[lrayvick]

Well, I finally broke down and took it to a friend who has a BMW code reader. He confirmed that the MAF is bad.

The readout also showed my trans shifting problem (will not go from 3rd to 4th in auto - have to switch to M to get it to upshift). He said it is internal to the trans. So I won't be spending the money to fix that.

The readout even showed my problem with the air conditioning - the compressor is bad.

Interesting stuff those BMW code readers. Much more detail than the on-board system.

Thanks again Ed.
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1994 530i Auto