An investigation of the clean-up effects of a Combustion Chamber Deposit (CCD) detergent additive package on tailpipe exhaust emissions was conducted using (6) 1992 2.3L vehicles. Part one of this program was a deposit build-up phase for all cars and part two included two phases where, in the first phase, one-half of the cars were operated with the CCD detergent package and the other half were run as a control on the build-up fuel. In the final phase, the fuels were switched between the sets of vehicles to compensate for any vehicle to vehicle differences. A gasoline containing a detergent package which provided port fuel injector (PFI) and intake valve deposit (IVD) cleanliness performance in accordance with California Air Resources Board (CARB) requirements was used as the deposit build-up fuel for part one and as the control in part two. This fuel is typical of many gasolines that are in the market place today. Using the same base fuel as was used for the deposit accumulation but with the substitution of the CCD detergent additive, the effects on tailpipe emissions were measured. Both additive packages showed good intake valve performance, with the ability to pass the BMW unlimited mileage requirement. The results of this investigation show that NOx emissions increased with deposit accumulation and decreased with the use of the CCD detergent package relative to the control fuel.