Purchased 2001 V70 XC

[Astro14]

The misfire is likely a coil pack. Swap them and see if the misfire moves to another cylinder. Fix the crumbling looms at the same time (common problem, easy to fix)

I wouldn't worry about the O2 sensor fix on older XCs (using an anti-fouling plug to move the sensor) - that doesn't seem to happen to the P2s much...if you've got a failed/failing coil pack, fix that first, clear the codes and see if this one returns.

Turbo control Valve is a common failure item, about $90 to replace from IPD, you might just consider doing that upgrade/fix.

Sounds like the car has been well maintained, the items above (coil pack, TCV) are common, but not hard or expensive to fix...

[Kitheme]

I forgot to mention previously, beside the minor problems mentioned I've been having hard start issues over the last two weeks. At first, I thought it was related to the O2 sensor code I'm getting, but could it be related to the coil and/or TCV codes?

... or do I have another fix to make?

[Astro14]

There is no boost present at start - turbo hasn't spooled yet, so it can't be TCV.

O2 sensor is also not likely - the engine is in "open-loop" during start, no O2 feedback.

Coil pack is a maybe - but only if it was misfiring every time...i.e. not working at all...

Hard start is more likely the cam angle sensor - but fix the coil pack first and see if it improves...any other codes present?

[Kitheme]

Didn't believe it could be a turbo issue, but thought I might ask just in case there was a weird connection. Was thinking that the O2 code might be the result of fuel getting past cylinder #5 as a result of the coil mis-/not firing...

... and it's amazing how much better the car drives after replacing it. It once again starts without me having to pump the gas pedal (though I feel like I hold the key longer than I should), and there's no knocking/pulsing at idle. Acceleration is much smoother. I still think that the car is not accelerating as rapidly as it should, but I have hopes that replacing the TCV will do the job. (I also have to remember that the car isn't exactly lightweight.)

Have to check the codes once again tomorrow (really need to buy my own reader), but last night it came up with P0030 (O2 sensor), P0234 (turbo overboost), P0300 (multiple misfire), P0304 (misfire in cylinder #4 [location coil was swapped to]), and P0305 (misfire in cylinder #5 [hadn't wiped codes prior to swap]). I expect that the last three will be clear now.

[Astro14]

Sounds like you're back in business...

Clear the codes. They all look related to a severe misfire. Three codes were misfire. That cylinder with the failed coil pack would be putting unburned fuel into the exhaust, causing the O2 sensor to be out of range. I am not sure if it would cause the overboost, but clear the codes and see if that one comes back. The other 4 should be fixed...