1992 740t wagon, 150k miles or so. The car is consuming approx. 1/2 to 3/4 of a quart of oil per 750-1000 miles and is losing coolant. The coolant reservoir will go from max. to min. in 3-4 days. It has a pretty steady stream of white smoke at idle that dissipates fairly quick (does not smell sweet)and does not start smoking it seems until the car warms up a bit, usually 3-4 minutes. There is no noticeable gain in smoke while under boost. The car throws codes 1-1-3 (fuel trim rich/lean) and 1-2-1 (faulty signal to amm). The car is getting poor fuel mileage,and with the exception of the oil usage runs and drives very well, good idle,etc.

Compression on the car dry w/no plugs, throttle wide open (front to rear)
145-140-155-160 (I did not inject oil and test)

When the plugs were removed all 4 were white, very white.

I recently repaired all the oil leaks associated with the oil filter adapter/turbo and related recently, but I still have a small drip at the oil cooler, on the long hose. This drip is somewhat odd because it looks like oil on the ground, and feels oily, but when under the car if you can see a drop hanging on the car in the light it will look green (like coolant).

Other than the drip at the oil cooler the car has no other oil or coolant leaks.

When the leaks were repaired, the (Mitsi) turbo was off, very little shaft play and was clean and looked like I suppose it should from what I could see inside. Very little oil in the intercooler piping.

There is no coolant visible in the oil, or oil in the coolant.

The oil seperator box was replaced less than 5k miles ago, all associated lines cleaned.

No vacuum leaks that I can find, sprayed intake w/carb cleaner, no change in idle.

The AMM has been cleaned from time to time, the car runs/idles fine and runs worse with the AMM disconnected.

I attempted to test the O2 sensor yesterday, but I am not sure I did this right. With the car running at temperature, I connected the multimeter + to the single wire connection of the sensor and grounded the - to the strut tower. The dc voltage seemed to oscillate from <1v to around 3 volts back and forth. I may have done this wrong. I do believe the sensor is probably contaminated and will need replaced. I do not know when or if it has been replaced.

I was thinking blown head gasket but the car has never overheated or offered to run hot in the 3 years or so that I've had it and the compression #'s while not perfect seem to indicate otherwise. Could some type of failure in the oil cooler or turbo itself allow for coolant to be get to where its not supposed to be and be burned (hence the white smoke)?

The car overall otherwise is healthy and has received regular maintenance and service for the majority of its life from what I know. Any ideas or help is appreciated. I figure some oil consumption is to be expected with the mileage/turbo combination but I'd like to solve the coolant/smoke issue at least.

Thanks