1992 400SE W140
The above car failed its bi-yearly emissions test a few days ago, the first test failed due to too high of a HC count at the ASM2525 test:

ASM2525 TEST
HC ppm
Limit: 45
Reading: 100
FAIL

CO%
Limit: 0.25
Reading: 0.08
PASS

NO ppm
Limit: 315
Reading: 0
PASS

RPM: 1800 VALID
Dilution 14.8 VALID

CURB IDLE TEST
HC ppm
Limit: 200
Reading: 132
PASS

CO%
Limit: 1.00
Reading: 0.37
PASS

NO ppm
N/A

RPM: 732 VALID
Dilution 14.9 VALID

So I did some research & asked around, to find out that the Catalytic Converters on these cars need to be heated up really well. So I ran the car at idle for 10 minutes at 2500RPM, and then let the tech do the test again. The results were completly different, this time failing with a too high NO count at the ASM2525 test:

ASM2525 TEST
HC ppm
Limit: 45
Reading: 5
PASS

CO%
Limit: 0.25
Reading: 0.00
PASS

NO ppm
Limit: 315
Reading: 956
FAIL

RPM: 1452VALID
Dilution 14.3 VALID

CURB IDLE TEST
HC ppm
Limit: 200
Reading: 4
PASS

CO%
Limit: 1.00
Reading: 0.00
PASS

NO ppm
N/A

RPM: 660 VALID
Dilution 15.0 VALID

Can anyone offer any input or suggestions as to where to start trouble shooting? As you may know, this car does not have the check engine light.

Thanks