2000 turbo XC70 with terrible idle and dreadful gas milage

Enid Puceflange · Post by **Enid Puceflange** » 26 May 2010, 07:38

OK, so the car has been pretty good so far, but just recently it developed a couple of, ahem, issues. The gas mileage dropped into the tens, which hurts, and the idle is VERY rough, hunting and varying from perhaps 900 RPM down to 600 or so. There's a lack of power, as well, and a STRONG smell of sulfur.

Pulling the codes, I got P0134 and P1174 (the 134 I understand - O2 sensor missing, but the other one I have no clue as to what it means).

This problem is intermittent - it first happened perhaps 3 weeks ago, and I was convinced by a knowledgeable friend that the problem was the MAF sensor - $60 and Ebay and it gets changed out, and for the next 5 days all is good. I drove to get my wife from the airport and just as I get there the rough idle and engine light is back. Doh!

The hoses seem in good condition, but I admit I haven't checked for a vacuum leak (like some of the posts on similar problems suggest)- any ideas where would be a good place to start (assuming it is a vacuum leak of course).

So - I'm at a loss. Any suggestions? Air filter is clean, oil regularly changed, car has about 96k on it. I'm not keen to change the O2 sensor on the off chance, but I'm also not keen on giving the local dealership a fat bag of cash either.

Post by **jblackburn** » 26 May 2010, 07:43

Sounds to me like your front O2 sensor bit the bullet.

The connections at the left side of the intake manifold are common suspects for fuel trim codes.

Enid Puceflange · Post by **Enid Puceflange** » 26 May 2010, 08:32

Thanks for the quick reply! I wasn't sure about the O2 sensor because the problem is intermittent - it was fine for 5 days or so. Is this a standard failure mode? How nasty a job is it to replace the sensor? Is there a good way to diagnose that it has failed before I lay out the cash (my wife accuses me of just changing parts at random until it gets fixed, which hurts the engineer in me but in this case it seems it might be true

)

Edited to add that I do have an Innova code reader - I'm just not sure what live data I should be looking at to decide if the sensor is toast.

Post by **jblackburn** » 26 May 2010, 08:59

You can plug in a scanner and read the values for it. It should hover around 1V at most RPMs; it will jump up and down as you push on the gas or let off.

Usually, though, terrible gas mileage and over-rich conditions means one of 2 things: MAF or O2 sensor. You may have made it happy for a few days, but was your gas mileage still lacking?

Does it work intermittently now, or just not at all? You could also try unplugging the MAF and see if the car runs any better. If that works, something is destroying them...hole in your air filter maybe? I've seen it happen.

Enid Puceflange · Post by **Enid Puceflange** » 26 May 2010, 09:09

Actually, now that you mention it I was watching the MPG meter after changing the MAF sensor and I was pretty disappointed that it didn't get better than about 18 or 19 mpg average - I put that down to the short hop driving though.

It seems to be intermittent - it worked OK for 5 days, then ran really badly yesterday, and when I took it round the block to see how bad it really was it seemed to be pretty good again.

One other thing that I'm pretty sure is unrelated - the car is often hard to fire up. It seems to crank for a VERY long time before firing up, but after that it is fine. The work-round I've been using is to turn the ignition on, then fasten my seat belt, then crank the engine, which works pretty much all the time. My guess is that this has to do with fuel pressure - I'm guessing that the non-return valve in the fuel pump has failed, so there's no fuel pressure until the pump runs for a bit.

I guess this car is determined to teach me about modern engine diagnostics.....I'll have a look at lunchtime and see if I can tell what the O2 sensor voltage looks like.

Post by **jblackburn** » 26 May 2010, 09:17

One other thing that I'm pretty sure is unrelated - the car is often hard
to fire up. It seems to crank for a VERY long time before firing up, but
after that it is fine. The work-round I've been using is to turn the
ignition on, then fasten my seat belt, then crank the engine, which works
pretty much all the time. My guess is that this has to do with fuel
pressure - I'm guessing that the non-return valve in the fuel pump has
failed, so there's no fuel pressure until the pump runs for a bit.

Yeah, sounds like it. The pump assembly is a total PITA to replace on an XC, so if that trick works for you, I'd be willing to live with it til the pump dies.

Since you say it seems intermittent, try putting a zip-tie around the connector on the MAF sensor. The older fasteners on the ones like my car tend to come loose after a few years, and can cause that to happen too.

Enid Puceflange · Post by **Enid Puceflange** » 26 May 2010, 09:49

Is there a good diagnostic I can watch with the ODB tool to check the MAF sensor? That'd let me know for sure if that was causing the issue when it happened......

Post by **jblackburn** » 26 May 2010, 10:00

Not on my scanner. When it starts acting up, you can unplug the sensor entirely and put the car in limp mode and see if it acts better.

Enid Puceflange · Post by **Enid Puceflange** » 27 May 2010, 07:11

OK, I went home and stuck the scanner on live data (after clearing another 134 code out). My Innova DOES have MAF, and the value goes up as you stick your foot on the gas, just as you'd expect. The O2 voltage, however, sticks at 1.084v no matter what, so I guess I'm up for a sensorectomy.

Never having done one of these on this car, where is it, what's the best approach to change it, and where is the best place to get a replacement?

Post by **jblackburn** » 27 May 2010, 07:31

It's on the downpipe that goes from the back of the engine to the cat. The front one's pretty easy to get to, just releasing the connector is a pain.

Get an O2 sensor wrench and a can of PB Blaster. Spray it down and let it soak for 20-30 minutes, and then have at it.

You'll need a Bosch genuine replacement - the universal fit ones aren't so good for these picky cars. Bosch online, or several of our suppliers at the top of the page sell them for decent prices, but they're still expensive.