Change timing belt. Cooling system maintenance is critical for the turbos. Drain and flush the cooling system. Refill w/ fresh antifreeze mix. If cooling passages in the block corrode and close up the head will warp and the gasket will fail. Replace the heater control valve. Remove and clean the throttle body and air bypass valve. Spray brake cleaner works very well. Remove and clean the oil trap under the intake manifold. Replace the o-ring. Clamp any loose vacuum line connections.