Tom,

I found no leaks whatsoever. So I decided to replace the front O2 sensor, since a person friend of mine had gone through the same thing in a 940. But checking with the autoparts store and Volvo the OEM parts went from $185 to $250 so I took yet another advice and bought an alternative O2 4-wire sensor from Bosch, the number is 15717 and Autozone sells it for $50.

Now, here's the trick, the wires are shorter and the connector is different, means you have to match the length, splice the wires and solder them for the existing connector.

I off course was very comfortable since I have a soldering iron and shrink tubing etc., so unless you feel you can do it or know someone that can help you then I would think twice before getting this part.

I wanted to wait a bit before I gave it a final conclusion, primarily because this was intermintent, so I still won't do it. However, the time between the last two occurrences has come and gone and the symptoms have not return yet. I immediately notice that the smell of unburnt gas is gone.

I hope this help and good luck
Rui