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There is widespread evidence in the literature that carbonaceous deposits can accumulate on the rear of intake valves and can adversely affect engine performance. For port fuel injected engines, a number of authors have suggested that the porous nature of these intake valve deposits (IVDs) means that they can act like a “sponge”, thereby preventing the correct amount of fuel from entering the combustion chamber during transient operation, especially when the engine is cold. A combination of experimental gas adsorption measurements and computational molecular simulations were used to characterize the porous structure of a sample of IVD. Molecular simulation was then used to predict the equilibrium adsorption of various hydrocarbons, including isooctane, in IVDs. The results support the theory that adsorption of fuel components in IVDs could perturb the mixture preparation.