Sounds like you have a case of sticking or worn exhaust outlet valve/s. As long as the engine ticks/revs fine with no adverse exhaust smoke associated with timing/fuel injector pump probs.
If the rocker/s is/are out of sync, the spent fumes can't access its normal path to the exhaust manifold, hence one way only, filler cap, and dipstick-the only unsealed ports of an engine. Ensure dash is'nt flashing/indicating warning/service lights.
robboWVH, April 2008
