Adrien:

I used to own a 740 gle before i got the 850 and i read up on the bestest FAQ on the cars in here:
http://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm

Even though it was about the 700/900 series, most of the symptoms/remedies are essentially the same. so i highly recommend you print and read out this section. you will start recognizing things in there. back to you question:

1. yes, ect is engine coolant temp. when the signal coming from it is bad, the computer thinks the engine is running cold and injects a richer mixture which causes revving. and then the computer cuts out the fuel supply to protect engine from over-revving.

2. good to hear that there is no buzzing which means your fuelpump is ok. yes you can buy the relay (i think it is a bosch) from the dealer. just mention your vin# so that you get the right part.

stalling is often caused by by a sudden interruption of fuel or spark so that's is where to focus.