Looking into the same thing myself at the moment and by most mechanics I've been told that the bearing in the turbo has a top feed for oil and a bottom oil drain, this can get blocked, also there is a filter before the oil gets back to the engine which can get blocked, so check the drain pipe and filter, filter may need replaced, at the minute your turbo could be burning up the oil that should be going back into your engine
Could be your timing belt.
What color is the smoke? Black - running rich. Bluish - buring oil. White - burning coolant. When you smell the gas, it is inside or outside the minivan? Back of the car or near the front?
exhaust leak or a possible fuel line leak
Plug wires installed incorrectly. Click the link.
Replace the Idle Air Control Valve only about $50. This would cause funny idling and stalling out.
muffler or exhaust could be damaged....if it has aftermarket exhaust it will sound different since it is not a V8.
Valve cover gasket.
Plugged fuel filter Plugged air filter Restricted exhaust (bad Cat)
I would think that you have a leak in your exhaust system.
Fuel delivery problems such as a dirty fuel filter, faulty fuel pump, faulty fuel pressure regulator. Restricted exhaust such as a faulty catalytic converter, crushed/bent exhaust pipe.
It is formed through the combustion proccess in the cylinders then exits thru the exhaust system so the tail pipe would be where it is emitted.
Check the idler pully.