My 1986 420SEL with 224,762 miles has failed VA emissions. Here are the test results:

15MPH Test
Test Limit Reading Result
HC ppm 65 149 Fail
CO% 0.26 0.23 Pass
NO ppm 857 375 Pass
RPM 1304 Valid
Dilution 14.6 Valid

25MPH Test
Test Limit Reading Result
HC ppm 119 229 Fail
CO% 0.38 0.35 Pass
NO ppm 833 623 Pass
RPM 1240 Valid
Dilution 14.6 Valid

Visble Smoke Inspection Pass


My question is: What would cause high HC readings and what are some things I should be checking for?
Thank you