Reduced power, bad gas mileage 2000 V70 XC S/E

[Varney]

When I first purchased this car about a year ago, it was peppy and got about 22MPG with "fun" driving. Somewhere around Christmas time I started noticing that she was getting a little weak. Then my fuel economy dropped to 17mpg all of sudden with no change in driving habits. I thought it might be low tire pressure, so I filled them up and there was no difference. Eventually I started noticing surging, I would get on the gas and I'd get a quick surge of power that would drop off quickly unless the RPM was ramping up fast, like after a downshift when passing on the highway. But off the line or from low speed, it'll pull good until about 3K RPM, hangout there for a moment and continue like a depressed teenager taking out the trash. I tried to test my TCV tonight, but found the vacuum lines to be too brittle to remove without breaking it off. I'll be replacing those as soon as I can. Not wanting to feel my time was wasted I took it for a run with the TCV unplugged and it was smooth (and slow) sailing through the RPM range. It seems like the vacuum lines are probably cracked and giving me grief, but I was wondering if there's anything else I should be testing, or looking for when changing the vacuum lines?

[FlyingVolvo]

Hello fellow 2000 XCer, welcome to MVS!

How many miles on the car? Do you know if the ETM (Electronic Throttle Module) is original? The 99-01 Volvos have ETMs that go bad after a certain time and will cause weird throttle response, surging, and eventual limp mode (usually associated with an "ETS" warning light on dash). You could be experiencing the first signs of this failure, but it could be something else as well.

It definitely does help to start with what you know needs fixing though. Interesting that it seemed to smooth out with the TCV unplugged. Check to see that the vacuum line on the compressor of the turbo hasn't fallen off. When it does, the turbo will generally spool up really fast and then blow off the pressure (ask me how I know!). If you still have your original AWD components (prop shaft and angle gear), this is a very pain-in-the-ass vacuum line to reach. Probably worth replacing them all though because your description makes them sound original. IPD sells appropriately sized color-coded silicone hose kits if you're into that sort of thing.

[Varney]

I have 160K on it. I don't know about the ETM. The car was dealer maintained before I got it so I can probably find out. Yes, I do have the complete AWD system, so that'll be such fun. I was looking at the IPD kit already and will probably go with those.

Further wrench to throw in the works, I went to clear the TCV code after plugging it back in and found a stored catalyst below threshold code. After clearing them both, the car went back to its happy self. I'm now thoroughly confused, but curious if any of that fits in with the ETM theory.

[FlyingVolvo]

I wouldn't worry about the catalyst code (P0422). I've had it on and off (mostly on) for the last 7 years. I finally just bought a rear O2 sensor spacer from IPD and have yet to have it reassert which is nice. I have no reason to suspect the cat itself is actually failed or clogged, so I'm quite happy with that fix.

Strange that things went back to normal after the codes were cleared. Keep and eye on things, because I suspect you may experience those symptoms again. Find out if the ETM was ever replaced (it's a matter of when, not if they will fail).

[bskeels]

How are your basics, fuel filter, plugs, etc. I replace the filters on mine every year and get some of my mileage back. Most of the northern states go to a winter formula in the gasoline that does seem to reduce mileage, to improve cold weather starting. I would replace your vacuum lines, as they sound a little hard and brittle, and the fuel filter and go from there.