1995 BMW 525i smog question

My BMW barely passed the smog test: 122,446 on the odometer, 79 ppm hydrocarbon measured and 81 ppm is the maximum allowable at 15 mph! At 25 mph, it was 34 ppm hydrocarbon measured and 46 ppm is the maximum allowable. The NO and CO emisions are about average at 25 mph and above average at 15mph but well below the maximum allowable. Before the smog, I changed out the air filter, spark plugs, fuel filter and O2 sensor. I have two years to figure out the problem before my next smog test but I like to solve it soon to reduce the emissions. What is the likely problem? Cat converter? Leaky fuel injectors? EGR valve? Other than the smog emission, the BMW runs fine with a very smooth idle and good power. Thanks