I have been reading some of these posts and find them very helpful, I just hope you have an as good solution for my dilemma.
Any assistance will be greatly appreciated.

I've been having this problem with my 740 2.3 Turbo, (137,000 miles).

Whenever I first start the car, even if I have driven it a few minutes prior; it has absolutely no power under load, especially going uphill.
The turbo gage goes way up high when I floor the gas pedal, but the car hardly moves; feels like it's starving for fuel or choking.
My mechanic has not been able to find a solution, he claims all the codes read normally.

When it first started doing this, what I would do is pull to the side of the road and shut the engine off, re-start it after a few seconds and it would drive like a champ, with power to spare until I got to my destination.
Then I would have to do the same procedure over again every time.

Lately, it has gotten worse,...... it will take some times up to four times (shutting it off and restarting it immediately after) for it to finally work normally.

What I have noticed also is that when it does this it leaks oil out of the right hand lower side of the motor onto the exhaust pipe, (have not been able to pinpoint where from exactly, since it is an oily mess underneath). When I park after a drive, smoke comes out from the under side, from the oil dripping on the exhaust pipe.

Don't know if this has any relationship to the above; in the lapse of 2 months apart, when I came to a traffic light and waited, I noticed very heavy bellowing of white smoke out of the tail pipe, and it slowly minimized and dissapeared as I drove off. It has done this two times in the 2 month period.

Any good suggestions?

I've been having the same issue lately and have been working to narrow it down. In my case shutting it off and restarting doesn't usually work, or it will work only if I let it sit until it cools. I have noticed this problem becomes more apparent with more passengers or load as well for whatever that's worth.

Given that I've replaced almost my entire fuel system over the last year I can rule that out as a possible source. I can also state that it isn't en exhaust issue since I've replaced the exh. manifold and my second turbo only has about 50k. I've adjusted the valve tappets, replaced the plugs, replaced all teh filters, and replaced the vacuum lines as well.

My thought is that it is a faulty knock sensor. I get a cherry turbo connector, but this can be normal under hard driving conditions so it's hard to take that as a sign the knock sensor is faulty. The only way I know to check is to pull the sensor and check it with a multimeter... if you get like 4.2 mOhms that is normal, if you get something ridiculously low the sensor is shot.

I've also though it might be the o2 sensor for some reason, but I'm planning on just replacing the knock sensor since the car is at 216k miles and I'm sure its near its life expectancy anyway.

Anyway, the "turn off to reset" symptom has led me to conclude that, whatever it is, it is electrical and most likely a faulty sensor. As bricks get older this problem can also become amplified by valve slap; it's possible a faulty knock sensor could detect slap as knock and retard the timing.

good luck,
rt

These symptoms sound like a knock sensor failure. Ignition will retard to a safety level if control unit senses faulty signal. Your car has limited self diagnostics in the ignition system only, archives here may have info regarding testing, or have your mechanic check it. Requires a special LED diode test light to be connected to test terminal and a flash code read after fault occurs and before ignition switched off.
Would have little relation to oil leak.