A few weeks ago, I had P0302 and P1171 codes come up. replaced #2 coil pack (never noticed a miss) and cleaned the MAF. It was a couple of weeks before I cleaned the MAF. Now, I have P0030 and P0135 - front O2 sensor. Mileage is gone way down and power is way off. I think my 96 855 n/a with 335K will stay even with it.

P1171 has not come back since it was cleared about 2 months ago, but I just cleaned it this week. If the MAF goes bad, is there a default mode that dumps a lot of fuel and could have fouled the O2?

If the O2 goes, I am sure there is a default mode that runs rich and causes fuel mileage to drop. Will it cause the performance to be way down?

Just trying to decide what to replace. O2, MAF or both. Oil is starting to leak quite a bit from the front of the car, so will be replacing the oil trap.

Thanks for the great input!!!

Keith

Bottom to top answer. Where is the oil leaking from???? If it is from one of the cooler lines on the passenger side, then the lines need new O rings. If it is from the front cam seals, that is a bear to replace.

Check the PCT nipple just infront of the turbo intake. It needs to be clean, when clogged it acts like a clogged PCV and drives the crankcase pressure up.

When the MAF fails it will go into default mode. Never unplug/plug the MAF with the engine running! Your air mixture will be seriously compromised with an incorrect MAF reading. Check for any air leaks before replacing the MAF, but save money for a new one.

Your O2 sensor needs to be replaced. But also check all of the vacuum lines for leaks prior to replacement.

Klaus
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I am not a mechanic, so can you trust what I type?

The leak is up front at the right side dripping out below the intercooler. There is no noticeable crankcase pressure or vacuum at idle. Back in the spring, I checked the hoses and connections around the turbo and everything was clean. The car will leave a table spoon or two on the ground overnight. There has been a slight leak at the cam seals when I put in the timing belt, but it has not changed. This front leak has been going on for about a year, but only a drip every couple of days.

Could be the since it has had a loss of power, the wife is driving around with her foot in it reducing vacuum and the leak kinda matches the timing of the CEL for the O2 sensor.

That spot of oil under the intercooler is from the weep hole. It will only leak when the turbo is at boost, which is consistant with your theory.
Time to put the air guide back on :)

Go for an O2 sensor.

Klaus
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I am not a mechanic, so can you trust what I type?