White smoke from exhaust - 3 shops couldnt diagnose the problem! Help!

2003 Mazda 6 - V6 - 80,000+ miles

For the last 6 months, my car would emit thick clouds of white smoke during start-up and sometimes idle.
The weird thing is that this happens randomly. For example, It would have intense smoking for 2 days, then it would be fine for 3 weeks.

I first noticed the smoke after a regular oil change at Pep Boys. I brought it back and they claimed nothing to be wrong.

Later (January), the check engine light came on. A/T light came one once as well but then went away after i restarted the car. I brought it to the dealership and they replaced the throttle body, the throttle body gasket, and intake hose. They cleared the check engine light. The said there was a leak at the oil tank gasket but isnt the reason for smoke.

I still saw the problem and brought it back two weeks later. They claimed nothing to be wrong and said it was due to the cold weather and condensation.

Frustrated, I put up with the problem for months. Now I am seeing the problem more often. The weather is hot now so i dont believe it is condensation. Not trusting the dealership, I brought it to the mechanic at a nearby gas station. He claimed he couldnt find the problem. He told me that without actually seeing the smoke, he couldnt tell. (I realized that everytime I brought the car to be looked at, it was during a time the car wasnt smoking)

After reading some stuff online, I have looked at a few symptoms. Can anyone try to diagnose the problem? (i still havent fixed the oil tank gasket)

Symptoms.
Heavy white smoke certain days during start up and idle.
No loss of coolant.
No milk-shake oil.
Bad gas mileage.
Car struggles to accelerate sometimes (especially during times of smoke).
Car acts jerky sometimes. (however, there are times of good response and acceleration from car)

quote:

ORIGINAL: arprok13

 Not trusting the dealership,

 
Is there another Mazda dealiership relatively close by? 

There should be, the problem is they charge nearly 200 dollars just to tear things apart and look for the problem.
last time i spent over 700 dollars and nothing happened. I just would like to know some ideas so that i can tell them or another shop

I don''t know what to say.  Not being an automotive expert by any streatch of the imagination, I''ll take a wild guess and say you need a new ECM.