Gasoline Port Fuel Injector (PFl) plugging is a relatively new and unexpected problem in the field. In the Fall of 1984, there was a large increase in car owner complaints about poor driveability at low mileages. This occurred in a narrow geographical area around Denver, Colorado. Most automotive engines with PFl systems are subject to the problem. The rate of injector plugging is primarily affected by the hydrocarbon composition of the base gasoline and the presence or absence of detergent/dispersant additives. Deposits that form on the injector pintle tips restrict gasoline flow to the cylinders. These deposits continue to build to a degree where engines misfire, run rough, lose power and are difficult to start.Most PFl engines use the same type injectors from a single major supplier which accounts for their similar susceptibility to the deposit problem. Detergent/dispersant gasoline additives provide an immediate and effective solution to the problem as demonstrated in the recently developed vehicle test described in this paper. The test has been generally accepted by other investigators. Base gasoline effects on performance in various car makes are presented along with gasoline additives both to keep injectors clean and to clean up dirty injectors.