1991 240sx: Failing emissions with high hyrocarbons and cabon monoxide at idle

[vancouverbc]

Did the fuel leak down test and found no leaks. Compression is normal. There is oil on the threads(not the tip) of second spark plug, though. All the spark plugs look similarly black. I did the o2 sensor test and it indicated I was rich at idle and over 2000 rpm. I past the driving test for emissions.I did have high oil level for emissions test. I had new oil for emissions test.The O2 sensor does not control idle so I didnt test o2 sensor. Replaced the coolant temp sensor.

[NISTECH]

plain and simple, your getting to much fuel at idle. HC's are unburnt fuel, CO's are partially burnt fuel. Our state samples tail pipe emissions differently so your numbers wont do me anygood unless they are in PPM and %. GPM wont do me any good for diag as I dont know the base line for those numbers.

When ever we have a failure for High HC's we look at CO's to determine if the HC's are due to to much fuel. If CO's are low then we check for lack of ignition, If they are high we look for excessive fuel. Things to check are fuel pressure regulator, coolant temp reading with a scan tool[to make sure its not in warm up enrichment] , airflow meter, and determine if 02 is biased lean[ since it passes during loaded mode this is not likely]

My 2 choices first would be number 1) airflow meter operation[check for hotwire contamination and voltage drop on ground wire] second would be leaking fuel pressure regulator into vaccum line.

[vancouverbc]

Thanks for the well thought out reply:) I will look at air flow meter next.