Intake valve deposits were characterized by chemical composition, thickness, density, porosity, hardness, and heat transfer effects. Data are presented to support the theory that high-load accelerations create deposits that may be primarily fuel related. A method to determine deposit thicknesses using a coordinate measuring machine is described. A finite element heat transfer analysis was undertaken to predict temperatures, estimate deposit thermal resistance, and demonstrate a method for modeling transient heating. The fuel-absorbing characteristic of deposits is examined in relation to warm-up driveability problems. Vehicle tests were performed to investigate the thermal resistance effect of deposits to poor driveability.