My 1989 420 SEL with 255,000 KM failed the provincial emission test. There is long list of what could be the problem. Here are the ASM tailpipe emission inspection results:

ASM 2525
HC PPM limit:50, reading:101, result:fail
CO% limit .28 reading:.18 result:pass
NO ppm Limit:548, reading:241, result:pass
RPM 1414 result:valid
Dilution: 15.6, result valid

Curb idle
HC PPM limit:200, reading:72, result:pass
CO% limit 1.00 reading:.08 result:pass
NO ppm Limit:N/A, reading:N/A, result:N/A,
RPM 665 result:valid
Dilution: 15.0, result valid

Engine coolant temp 85c.

I was told the high HC during driving test or high idle causes could be:

vacuum leak
ignition system malfunction
faulty computerized engine management system and or oxygen sensor
faulty air injection system
internal engine problem
failed catalytic converter

In November 2005, I had a valve job done, new intake manifold o-rings, new chain and guides, new plugs, air filter, new head bolts, mercedes gaskets, oil change was about 1,000 KM ago, using 5w50 synthetic. o2 sensor is about 3 years old. Prior to valve job, had a rough idle. Mechanic who did valve job said definately part of the rough idle job problem was the 0-rings, they were hard`as rock, also said the my ezl was OK.

The car runs great!

Any ideas?

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1989 420 SEL