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Ryan12345d
08-02-2008, 01:22 AM
Hi, i recently changed the headgasket on my 91 535i with an m30 motor. however it runs very rough when i start it up cold (almost as if its going to stall and when i put it in gear it jerks around a bit, but once it gets warm its fine) one thing im not 100% sure on is, there are 2 sensors ontop of the thermostat housing, just behing the bleed screw.Both sensors have the same 2 pin plug but there is 1 that has black plastic, and the other one has a light blue or green plug. On the wiring loom that meets upto that area, there are 2 plugs, a blue one and a black one. i just assumed the black wiring plug goes onto the black sensor and the blue wiring plug goes onto the blue/green sensor. Does anyone know what these 2 plugs do?will it matter if they are the wrong way around?could i have them the wrong way and the car not be riching up the mixture while cold (therefore running rough) the gauge operates fine though and only gets to the middle. i swapped them around (black wiring onto blue/green plug and blue wiring plug onto black sensor) and ran the car for about 30secss, and once again the gauge was showing the middle. i guess i will just leave them how i last set them and try again tomorrow and see how it runs cold?If anyone could let me know what these 2 sensors do, and as which loom plug should be on which sensor (i forgot to mark them when i took the head off, and didnt know they were the same plugs until putting it back together)
Cheers
Bruno
08-02-2008, 05:50 AM
One sensor is for the DME to know the coolant temperature and to add more fuel when the car is COLD.
The other one is for the gauge inside the car.

I never remember which one is which... but one plug should have the color of the sensor (The blue one maybe).
Ryan12345d
08-02-2008, 08:15 PM
One sensor is for the DME to know the coolant temperature and to add more fuel when the car is COLD.
The other one is for the gauge inside the car.

I never remember which one is which... but one plug should have the color of the sensor (The blue one maybe).

Hi, i swapped them over and tried starting the car this morning from cold, but i think it ran a bit worse?? if i rev the car and let it idle for about 1min its fine, i can then put it into gear without any jerking. but if i start the car from cold and put it into gear it runs really rough.
Bruno
08-02-2008, 08:55 PM
Hi, i swapped them over and tried starting the car this morning from cold, but i think it ran a bit worse?? if i rev the car and let it idle for about 1min its fine, i can then put it into gear without any jerking. but if i start the car from cold and put it into gear it runs really rough.

You can test the sensor with the values from the Bentley manual, could be a bad sensor.
Ryan12345d
08-02-2008, 09:16 PM
You can test the sensor with the values from the Bentley manual, could be a bad sensor.

I dont have a bentley manual, does anyone have the specs and how to test this sensor?could it also be a problem with the idle valve?or would this effect it when the motor is warm as well?it only runs rough when i start it from cold in the morning, and it doesnt blow smoke or anything so i doubt it is a leaking injector.