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Old 12-04-2012, 09:33 AM   #19
Parts hoarding partner...
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Join Date: Nov 2007
Location: Toronto
Posts: 3,429
Originally Posted by RedEye View Post
Could be the coolant temp sensor (the one that feeds the ecu, not the gauge. The blue one iirc). After I fixed all my vacuum leaks the surging stopped but the car was running so rich it wouldn't warm start. The resistance of that sensor increases as temperature decreases; the sensor's internal resistance also increases with age and wear. So an aging sensor can be telling the ecu that the engine is a lot colder than it really is, hence running rich. When I got my car I think it was only running because the vast amount of unmetered air from the many vacuum leaks sort of balanced the vast amount of extra fuel from the dead CTS.
I do remember swapping that some time back with a used one. that does seem to make sense. it is running rich for sure. Well, that may need swapping out for a new one. However, the sensor is brass and the only resistance it could bring with it is the tarnish? that can easily be cleaned up with a wire wheel. I think the sensor is like 15.00 -20.00 at most. Worth a try. thanks for the input.

I think I've had 18 bmw's in 6 years.

1 90 325is white - keepin
1 87 325i vert -red - keepin
latest addition 1 88-325is red - parts
latest addition 1 89-325i vert - white -fixin/sold
latest addition 1 92-318i vert - blue - parts
latest addition 1 87 325is blk - parts.
latest addition as of 2013-Gold 87-325is auto! it's a keeper!
KEEPER 88 5sp Vert 2016
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