super rich fuel mixture


Asked by Dec 22, 2012 at 01:52 PM about the 1990 Volkswagen Passat 4 Dr GL Sedan

Question type: Maintenance & Repair

Hi, I have a 90 Passat with the 2.0L DOHC and recently installed a K&N OE replacement filter wich did wonders for fuel
economy and performance but then i had issues with my cateletyc converter. I wanted to get a little more performance out of
it so my dad and I tokk the cat out emptied all the baffles so it is completely hollow now and then we put it back on. i noticed a
drop in fuel econemy but the car was running fine and it sounded great and it did just what i wanted it to do with

now for the issue, ive noticed with winter coming as the temp drops below 50 F the car is idling super high and not dropping
until i drive for 20 minutes or so ive also notice my fuel econemy plumit. ive checked the plugs and they show small amounts of
carbon deposites and a strong smell of fuel. my exaust also smell very rich.

so i was wondering if i opened the system up to much or i forgot to adjust something for the more open system.

-- thanks in advance

3 Answers


How is the coolant temperature? It sounds like the thermostat might be stuck open. If the temperature is up where it should be, try replacing the upper O2 sensor.


Temps fine ill take a look at o2


The cat creates backpressure which helps the o2 sensors get a correct reading (maybe the running rich). It only uses those sensors after it warms up a bit (maybe the 20min thing). Also is the K&N filter oil charged? It will or may have already damaged the MAF.

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