SRR2
03-30-2005, 01:13 PM
The background of this problem is summarized here: http://www.bimmer.info/forum/showthread.php?t=10762
It turns out the the throttle position switch is intermittent. It was cold every time I tested it, but this morning after yet another test drive I looked at it once again and found that it didn't seem to close reliably. Heated with a hair dryer, it stayed open. Interestingly, it has a pronounced 'click' when at idle position, but apparently the contacts in the microswitch aren't getting the message. After playing with it for a while, it now refuses to close at all. Since this commands the ICV, the symptoms now make sense, although why it chose to act up at the very time I changed the battery is beyond me.
Also, some information on the AFM. First, the Bentley book has the connector numbered backwards, and there is no pin-5 on my AFM. Pin 4 is ground for the pot and thermistor. I connected a 3VDC battery supply - to pin 4 and + to pin 3. The voltmeter - lead went to pin 4 and + lead went to pin 2 which is the pot wiper. Moving the vane produces a smooth change in voltage from about .2V to 2.8V, indicating the the AFM is probably working correctly. The reason the resistance reading behaves peculiarly as I described earlier is that the pot must be trimmed with some fixed resistors from + and - to the wiper, so you don't read the actual resistance of the pot, you read a resistor network instead. The voltage test I described is definitive.
It turns out the the throttle position switch is intermittent. It was cold every time I tested it, but this morning after yet another test drive I looked at it once again and found that it didn't seem to close reliably. Heated with a hair dryer, it stayed open. Interestingly, it has a pronounced 'click' when at idle position, but apparently the contacts in the microswitch aren't getting the message. After playing with it for a while, it now refuses to close at all. Since this commands the ICV, the symptoms now make sense, although why it chose to act up at the very time I changed the battery is beyond me.
Also, some information on the AFM. First, the Bentley book has the connector numbered backwards, and there is no pin-5 on my AFM. Pin 4 is ground for the pot and thermistor. I connected a 3VDC battery supply - to pin 4 and + to pin 3. The voltmeter - lead went to pin 4 and + lead went to pin 2 which is the pot wiper. Moving the vane produces a smooth change in voltage from about .2V to 2.8V, indicating the the AFM is probably working correctly. The reason the resistance reading behaves peculiarly as I described earlier is that the pot must be trimmed with some fixed resistors from + and - to the wiper, so you don't read the actual resistance of the pot, you read a resistor network instead. The voltage test I described is definitive.