Just failed an emissions check (I am stuck on this one-interesting question)

[spoolin318i]

So I just got back and everything checked out great besides the hc (PPM) low speed run.


My numbers are as follows

Pollutant High speed/Low Speed
HC (PPM) - 123/192 Standard (168/173)
CO(%) - .53/.64 Standard (1.08/0.98)
CO2(%) - 14.5/14.2 Standard (None/None)
O2(%) - 0.1/0.5 Standard (None/None)
NOx(PPM) - 444/868 Standard (1208/1323)

Any thoughts on why one could fail the low speed but ace the other tests? I am really confused here :(

[jlevie]

Is the idle smooth or lumpy. A lumpy idle probably means misfires, which will cause high HC.

[ptownTSI]

high HC comes from unburned fuel. change the O2 sensor, plugs, ignition cap/rotor if they haven't been done in the last 40k miles or since you bought it.