Results of numerous vehicle tests indicate that both unleaded and leaded gasolines when formulated with adequate dosages of an effective detergent additive can provide both port fuel injector (PFI) clean-up and keep-clean performance features even at very severe operating conditions. Significant reductions in flow restriction due to PFI clean-up were observed with several detergent additized fuels. The premium fuel additive dosage demonstrated rapid injector clean-up in relatively short mileage. The regular fuel additive dosage demonstrated excellent injector keep-clean capability even in relatively unstable fuels. Improvements in acceleration rate (10 to 161), driveability and idle quality were also observed associated with PFI clean-up.Results from nine vehicles tested at both controlled and consumer test conditions indicate that engine and injector design, driving cycle and fuel quality are key factors influencing deposit build-up.