The inlet manifolds are prone to air leaks causing the mixture to be weak when cold, but this also makes them over fuel and smell of fuel. The engines are not the most efficent. Its always worth having a diag tool run on it to check the function of the coolant sensor from cold to make sure its performing as it should. This can be read in live data.

The manifold tends to leak air around number 4 cylinder and also check the brake servo for leaks.