I have searched previous threads and have found some good information, but wanted to get a take on this specific issue.

Some time back, my '99 V70 started fluctuating RPMs at idle. I cleaned the MAF sensor and the problem resolved for a bit. Then a couple of weeks ago, it started doing the same thing. I cleaned the MAF without resolution of the problem. The car has about 130K miles on it so I ordered an MAF and decided to go ahead and replace both O2 sensors (ordered Bosch Universal Sensors). During this time I had also ordered some suspension parts that came in before the sensors and so used what little spare time I have making those replacements. Then, about a week or so ago when driving home from the store, the car suddenly started fluctuating RPMs and losing power at driving speeds. I was able to keep the car going by feathering the gas pedal to make it home. Along the way, the car would sputter and try to stall, I would feather the gas pedal and then it would pick up and run normally for about 45 seconds to a minute, then the loss of power would occur again and the process would start over. Once I got the car home, I let her sit for a bit and then went out to try to start her. She would start just fine, run at normal idle for about 15 or 20 seconds and then start to sputter and then shut down. Subsequent attempts to start resulted in shorter idle times before sputtering and shutting down until it would only turn over and not fire. I decided to let her be until I could get the new sensors installed, which I did last night. After getting everything back together and double checking everything, I tried to start her with the same result as before. I will be checking the fuel pump relay when I get home today, but would appreciate any other suggestions that you all may be able to give.

I also noticed that there is a failure in the ambient temperature sensor. I thought that this was simply to relay the outside temperature to the outside temperature reading on the dash. Would this sensor affect the problem mentioned above? The only reason I ask is that I have seen this sensor referenced in several threads and am not beginning to question my assumption that it isn't an important problem.

Thanks in advance.

Benny

 

In addition to replacing the O2 sensors (both) and the MAF unit, I have now Cleaned the throttle body and checked the fuel pump relay. Next is to check the fuel filter. I really need some help on this one. C'mon, somebody out tere must have had a similar problem and can suggest something. I don't have a fuel pressure tester or I'd check that next.

Oh, by the way. NO codes at all are being detected.

 

Okay... Here's an update.

The next thing I did was to check the fuel pump which was functioning properly. Then I checked the fuel filter. It looked pretty old, so I went and picked up a new one installed it and after a few tries, the car started up and stayed running. There was a little sputtering while the system came up to pressure, but it all smoothed out after a few minutes. I let the car idle for about 10 minutes and then shut it down. I checked for codes and pending codes and found none. I restarted the car and drove around the neighborhood. Things were going so well, that I took her onto the main drag in town.....still good....next I got on the interstate and took her up to speed....no problems whatsoever. Drove back home and announced to my wife that the car was fixed. She went out and got in, backed out of the driveway and before she got out of the neighborhood, the power loss thing began again (loss of power with feathering of gas to keep her going followed by a period of normal operation followed by loss of power...etc.) She gets the car back to the house, I put the code reader on it and now its saying that there is a permanent failure of the forward (upstream) O2 sensor.

Would this O2 sensor cause this kind of problem. I am beginning to get pretty frustrated and would REALLY appreciate some help with what to check next. The O2 sensor that I used was a Bosch Universal, could this be the issue?

 

New fuel pump relay has resolved the problem.