Certified GKH Gardening Expert
Generally, yellowing of the leaves is often attributed to too much water, which can also spawn fungal infections. The brown spots can result from water that has splashed on the foliage or fungal black spot. Back off on water and see if it helps at all. If not, the problem is likely due to a fungal infection and the plants will usually not survive. However, impatiens propagate easily so it may be possible to clip a healthy cutting (or two) and root it in case replacement of the plant is necessary.
Possibly too much sun, too much or not enough water.