OK, this thing has been about to drive me crazy. Here is the timeline of events:

1. Got the car and it ran like crap. Pulled codes and it pointed to the mass air. Replaced mass air, performed ECU reset/relearn. Car went into boost and would break the tires loose. Ran great. Got 28-31 mpg on the highway.

2. Months pass and is seems that the boost is getting less and less. Assumed it was mass airflow sensor. Replaced it under warranty. Boost back. Weeks later, boost/power seems to be going away.

3. Warranty mass air again. This one is a dud out of the box, car would not even complete a relearn.

4. Got money back on reman mass air and bought a new Bosch unit (from Oreilly auto parts, not Volvo; figured it's new, has to be the same? Maybe not...) and installed. Car runs like it should again. Took on long trip and it threw a light for O2 sensor. Installed new Bosch upstream sensor. Did not seem to change anything but light stayed off. Still lack of power.

5. O2 code came back again. Now assuming it is the rear O2 and it's not close enough to the front O2 to make ECU happy. Reset code, replaced mass air. Power back. One week later, power going away again.

Anyone have any clue? Is the O2 sensor making it pull back power as the LTFT's are learned? Can't remember my freeze frame exactly but I think that LTFT's were showing -2 and STFT's were +4. Will replacing both O2 sensors with new Bosch pieces somehow finally fix this problem? Love the car and just want to make it right....

Thanks in advance for the help.

 

I'll bet that you're using a K&N or other "serviceable" air filter.

If so, take it out, throw it as far away from the car as you can, and stick in a good ol' paper filter. The oiled filters are infamous for getting the element in the MAF sensor covered in oil, which of course messes with all the other parameters because of the GIGO computer concept (Garbage In, Garbage Out).

This is the first modification I made to my V70 (leaving the K&N filter in the Autozone trash barrel, and putting in a paper filter). Even under "laboratory conditions" (where they've probably under-oiled the filter to the point where it's not filtering sufficiently) any horsepower gain is minuscule with an oiled filter, and the down side is (to me) not nearly worth the potential issues.

 

Actually, the car is bone stock. Still has paper element air filter in it.

 

Dang... so much for the easiest fix in history...

I'd still recommend (strongly!) getting a can of MAF cleaner and spraying the element in your MAF sensor next time your power goes away. If that fixes it (quicker and cheaper than another new MAF sensor) you'll know that something is fouling the MAF sensor (not sure if crankcase blowby is routed so it could be the culprit or not, but you probably want to check your PCV system to see if it's up to snuff anyway - lots of info on that out there so I won't bother blathering on about that).

 

PCV system is good to go. Mass air sensor looks brand new inside and absolutely dry. I have read somewhere that the O2 sensors can make the ECU second guess what the mass air is telling it. Have also read that the rear O2 sensor does a lot more on these cars than most vehicles (most just tell ECU whether or not the catalytic converter is working...) and it will actually change fuel if the front and rear O2 sensors are not what it wants to see. Front is new so I guess I just need to put a rear in and see if that goes away. It will periodically throw a code for "manufacturer specific air/fuel". While reading up, says it could be the MAF, front O2, or very likely rear O2.

Looks like the rear is probably easier to do than the front....

 

I have a California car so it has a steel gas tank. I am guessing due to the emission regulations in this state.

But many other states these cars are sold with plastic gas tanks and they have a fuel filter that can be seen from the outside and needs to be replaced from time to time.

I would check that as a possible problem. Especially since you are saying PVC system is good.

 

Fuel filter is exactly where you said and I have already changed it. This thing is starting to make me scratch my head. Runs fine as it is, just does not have the power I've been used to it having.

 

The thing I was keying in on was that it seemed that every time you changed the MAF sensor, everything went back to normal. It might be interesting to see if just unplugging the MAF and plugging it back in would cause any improvement. Or at the very least, I'd try another ECU relearn (haven't tried that myself - will wait until I fix the shift solenoids first). Otherwise, I'm kind of at a loss how just replacing a MAF would cause an improvement in power for such a short period of time (unless, as I guessed earlier, it was being oiled by the K&N filter).

Or maybe it's just a coincidence. Or it's possessed. ;-)

 

OK, pulled up a couple pics I took of the code; maybe this will help:

P1132 MFR CTRLD fuel and air metering

Freeze frame data:

Engine RPM 1120
Coolant temperature 158
Speed 42
Calculated engine load 1.6
Long term fuel trim 7.8
Short term fuel trim -8.6

Above was in February. Not sure if this was during warm-up or if this is before I replaced the thermostat that was stuck open. In Feb, replaced timing belt, tensioner, idler, water pump, spark plugs (with correct copper plugs), fuel filter, air filter, oil change, ignition coils (Beru coils).

Either way, the more recent one was very similar in freeze frame. LT and ST fuel trims were nearly 180 apart. I think this past time it may have shown 4 and -4.

Plan on checking voltage to MAF. Wondering if it could possibly be a little too much and it's damaging the MAF. Need to get the O2 sensor replaced so I plan on just putting two new ones in again to make sure they are both reading similar.

 

Well, I did some looking and it appears that the O2 I replaced last year was the REAR O2. From what I can see, P1132 is front O2 sensor. Ordering that one tomorrow and I'll install it and do a reset and see if things finally come into line. I'm hopeful that this will finally get it back to where it was. Fuel economy is slightly suffering (23 or so around town and 28 on the highway where it used to get around 25 in town and 29-31 on the highway) so O2 sensor would make sense.

 

That DOES make sense - while the rear O2 sensor is pretty much only concerned with how well the cats are doing their job, the front one can really mess with your fuel/air mixture and performance. Keep us posted on your progress... it's my understanding that an O2 sensor will tend to be pretty much past its expiration date after 100,000 miles. I've gotten more than that out of some of 'em, but given how expensive gas is, and how relatively inexpensive a new O2 sensor is, it's a false economy to leave one in place if there's ANYTHING going on with the performance or fuel economy of the car.

 

Front O2 sensor is here but the rear is probably another week or so out. I will swap them both out at the same time and post back with results.

 

Replaced front and rear O2 sensors last weekend. Appears that car is back to normal now.