Vacuum leak or faulty O2 sensor?

[SteveT]

This is a continuation of a previous post...thanks to all who replied. I had been getting bad fuel mileage on my '98 S70 GLT (84k miles) to go with a strong gas smell coming out of the exhaust, but no CEL. After being advised by different people I decided to first look at vacuum leaks as the source of my problems, causing a rich fuel-air mixture (contributing to my belief that this was my problem was the fact that my cruise control works intermittently). The first elbow I checked was the first one on Bay 13's vacuum joint repair guide, the one on the passenger side of the intake manifold that regulates the turbo wastegate (or so I'm told). I broke the hose back in the engine. I ran the car like that for about 10 days until I made the repair, during that time I had a rough idle and the CEL eventually came on, no surprise. The strange thing is, the rich fuel-air condition became corrected...good mileage and no gasoline smell coming from the exhaust. Can someone explain this to me? After repairing the hose the rich mixture problem immediately came back. I check all other vacuum elbows I could find and they all looked to be in good condition. I also checked the vacuum hoses under the battery tray, the ones controlling the cruise control, and could find no problem. I had the engine codes read, getting only a "172 - System rich" code. I decided it was better to live without the turbo (i.e. leave the vacuum hose disconnected) until the underlying problem was corrected. Does anyone have any ideas as to where I can look before I drop a bunch of money on new O2 sensors (I also removed the pre-cat O2 sensor and it looked OK as far a white deposits go)? Thx.