Intake valve sticking, created by the accumulation of deposits on the valve stems, caused cold starting problems and engine failures at low temperatures (below + 5°C). Sticking was promoted by the high olefin content in gasoline (over 25% FIA). Sticking did not occur if gasoline contained no detergent additives. Some additives even led to sticking while some solved the problem. Engine oils containing polymeric additives promoted sticking.Clearances of intake valve stems and stem seals were probably factors affecting sticking. Tests were made using cars on the road on an urban driving cycle.