The exact determination of air/fuel ratio for dynamic response of today's modern spark-ignition engines, makes them more sensitive to the effects of intake valve deposits.The intake valve deposits work like a sponge and absorb the injected fuel during acceleration, which leads to a leaner air/fuel ratio. Non-uniform running may occur during engine warm-up and acceleration periods. The poorer running behavior of the engine increases the emissions and shortens the life time of the catalytic-converter. An increase in fuel consumption results.A laboratory test procedure was developed and used to evaluate the liquid fuel's tendency to build deposits on the intake valves. A dynamometer cycle was used to reproduce the intake valve deposits. The intake valve's temperature was measured during the test cycle. The critical temperature range for gasoline deposit build-up was determined /1/.