Has been through twice now and looking for possible causes. 1st test results only the 15mph test failed HC too high.
15mph HC=60 CO=0.12 NO=172
25mph HC=23 CO=0.04 NO=42
Afterwards, I smoke tested the intake and replaced a leaking oil collector and also replaced the spark plugs.
2nd test results both 15mph and 25mph failed HC too high.
15mph HC=89 CO=0.07 NO=68
25mph HC=74 CO=0.04 NO=14
Frustrating to have it fail worse after working on it!
It is fairly low mileage (138k) for a 1997. I am thinking the 02 sensor or MAF cleaning might help. It may be time to check the VANOS (variable valve timing) seals but I don't think the VANOS would be involved at these lower speeds.
Any help diagnosing possible causes would be welcome.