Per a post from about a week ago I am trying to track down a lean cold start condition in my 1985 745t. Basically the car runs lean and the timing is retarded in boost when the engine is cold, but everything normalizes when it warms up. The problem is engine AND ambient temperature sensitive, meaning it will happen only if the engine is cold and it is cold out.

What I'm wondering is if someone can tell me what happens when a cold engine starts up in, say, 40f. What is the order of electronics turning on? What handles initial mixture settings? Does the o2 sensor kick in immediately or only when hot? If the latter what establishes the default state? What's the ECU's role, just as the center of all reporting and trigger puller for mixture?How does the AMM figure into the picture when the engine is cold? Might a failing AMM be temperature sensitive?

I'm thinking its either the AMM or the o2 sensor, but I figure knowledge of how everything interrelates may allow me to identify possible weak points.

Thanks in advance for any help.

-rt