Deposit formation on the intake valve of spark-ignition engines is a well known and old problem. The intake valve deposits work like a sponge and absorb the injected fuel during the 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 of catalytic-converter. An increase of fuel consumption would be followed.A laboratory test procedure was developed and used to evaluate the liquid fuels tendencies to build deposits on the intake valves. This test method has shown a great accuracy and is very reliable. It can help accelerate development of additives. It can also be used as a pretest method for gasoline quality control. Chemical analysis and comparison between the results achieved by this method and the deposits from the intake valves show a great similarity of the substances found in the deposits.