Odd problem, '89 735ia running lean and stalling

[Bruno]

The customer is complaining that the car stalls when he stops at red lights.
When I checked the plugs (NGK R) and they were white.

The car idles without any problem and I couldn't get it to stall on me...
No vacuum leaks, fluids are ok. No check engine lights codes.

Weak fuel pump??

I am planning on doing a complete tune up (short of an O2 sensor). What would cause the car to run lean like that???

[MarkD]

The customer is complaining that the car stalls when he stops at red lights.
When I checked the plugs (NGK R) and they were white.

The car idles without any problem and I couldn't get it to stall on me...
No vacuum leaks, fluids are ok. No check engine lights codes.

Weak fuel pump??

I am planning on doing a complete tune up (short of an O2 sensor). What would cause the car to run lean like that???

Bad FPR or fuel filters?
Have a look if the car has a stock chip or something else.
How does it run in PT and WOT?

Does it stall when he stops at GREEN lights?

Mark

[winfred]

low fuel pressure possibily, but that can also make them go rich from bad spray patern, slow o2's generally show up as a surge at full throttle, dirty throttle body/icv?! dirty trace in afm?! not too many things won't trigger a ce light and make it run bad

The customer is complaining that the car stalls when he stops at red lights.
When I checked the plugs (NGK R) and they were white.

The car idles without any problem and I couldn't get it to stall on me...
No vacuum leaks, fluids are ok. No check engine lights codes.

Weak fuel pump??

I am planning on doing a complete tune up (short of an O2 sensor). What would cause the car to run lean like that???

[gale]

Check the temp sensor for the DME, it's the blue one nearest the head on the thermostat housing. Unplug the connector and measure the resistance across the 2 pins on the sensor. It should read in the neighborhood of 2100 ohms when cold and 270-400 ohms when at operating temp. If it reads less than 100 ohms, then it could be leaning out the fuel mixture to the point of stalling. If it reads on the low side, you can cut & splice the appropriate value resistor in series with one of the leads, 1/2 watt is sufficient.

[632 Regal]

Check the temp sensor for the DME, it's the blue one nearest the head on the thermostat housing. Unplug the connector and measure the resistance across the 2 pins on the sensor. It should read in the neighborhood of 2100 ohms when cold and 270-400 ohms when at operating temp. If it reads less than 100 ohms, then it could be leaning out the fuel mixture to the point of stalling. If it reads on the low side, you can cut & splice the appropriate value resistor in series with one of the leads, 1/2 watt is sufficient.

[MarkD]

Coolant temp sensors tend to make the motor run rich when they break since in the most common failure mode, the sensor resistance goes up. It's better to find the cause and replace the sensor if required.

Mark

[Bruno]

Check the temp sensor for the DME, it's the blue one nearest the head on the thermostat housing. Unplug the connector and measure the resistance across the 2 pins on the sensor. It should read in the neighborhood of 2100 ohms when cold and 270-400 ohms when at operating temp. If it reads less than 100 ohms, then it could be leaning out the fuel mixture to the point of stalling. If it reads on the low side, you can cut & splice the appropriate value resistor in series with one of the leads, 1/2 watt is sufficient.

Thanks I will check that out.