The cat was repalced in 96 with 70k and you now have 228k looks like the replacement did its job.

How much oil do you use? An old cat burning oil will need to be run at better than idle speed to keep the cat lit off. if the replacement cat wasn't a MB cat I doubt it is doing anything now.

We have never had testing in our area so I don't know test procedures but the car should be warmed on the dyno for a brief period before the test is run. If you are in the car while it is waiting I would hold the idle to 1500-2000 for a minute just prior to testing.

There was some testing done in Florida but it was just idle testing. There was a dyno at every station though. its use was to precondition the cat by driving under load for a brief time.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician