Here are some general tips to reduce emissions at test time:

1) Change oil and filter just before going to the test station. This reduces emissions from burning oil.

2) For my part, I would use an oil additive like STP Oil Treatment to thicken the oil a bit and further reduce emissions from oil smoke.

3) Have the car fully warmed up before testing.


And in your case it does look like the EGR valve could be responsible. Does the car generally run well? If so, I expect the EGR valve may be stuck closed - carboned up all around it. You'll need to remove it and clean out the passageways leading to and from it. Also check the vacuum hose leading to the EGR valve to make sure it is still attached. Some people disable the EGR system, and that has an impact on gasolene engine emissions testing.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles