There are several possibities, depending on how it's acting: valve stem seals, piston rings, leaking rocker gasket that allows oil to drip onto the exhaust manifold, leaking transmission vacuum modulator that dumps transmission fluid into the intake. If it's valve stem seal when you use the engine to slow down then when you speed up you'll get more smoke for a few seconds. If it's piston rings you'll often get more smoke whenever the engine is running. If it's the rocker gasket, it will smoke from the hood. If it's the transmission modulator, check the vacuum line from the transmission to see if there is oil in it.