Start with the basics- check your air filter and fuel filters. Timing might be off, or you may need to pull the injectors and see if one is clogged a bit. Color of the smoke indicates what it is- blue smoke means you are burning oil. White smoke may indicate that you have coolant mixing with the oil, black smoke indicates you have a lack of air or an abundance of fuel. Those are generalizations and only rough guidelines- there are exceptions to all three colors, and other causes for all three colors. Grey smoke may be incomplete combustion. If you watch large OTR (over the road) trucks you will see when they change gears there may be a lack of smoke or and abundance of smoke, but it is almost never steady. Try to give us a better description of a "wad"- is it so much you cannot see the car behind you? How long does it last?...etc.
After a report of the smoke color and state of filters we can give a better analysis of what may be the cause and steps to take to rectify.