The reason your Toyota 4Runner produced high HC emissions only during the 15
mph part of the smog test and not the 25 mph part is because the smog test
is designed to place a predetermined load on your Toyota's engine while it
is being driven on the dynamometer. At 15mph this load is twice (50%) as
high as during the 25mph test (25%). The added load on your 4Runner's engine
during the 15mph part of the smog check will cause it to work harder and
produce more emissions. The smog inspection is set up this way in an effort
to simulate real word conditions.
Since your Toyota came very close to failing during the 15mph portion, and
it produced marginal emission levels during the 25 mph portion we'd have to
recommend you have it inspected by a smog check repair station and have them
diagnose these faults, incluing the almost failing HC results. It is not
normal for a vehicle to produce HC close to the smog check cutscore. In fact
if you look at your Toyota's smog check VIR, you'll probably notice HC
average results closer to 10 ppm. Your Toyota's CO and NO are high as well.
