2000 V70R light surge at speed

[John850GLT]

Probably looked up an old Beetle: pliers and no time at all.
5+ certainly sounds more like it, plus diaphragm replacement. Gads, I'll have to crowd-fund it.
Disconnected both battery terminals and tapped together; disconnected/reconnected solenoid, and tapped with the 10 mm. I figure it's a solenoid that actuates a tiny gate or piston inside; maybe it's stuck or balky.
Drove it. Peppier, but not out long enough to get a sense of total effect.
Find out next week. Love the car, but.....

[John850GLT]

I'm not 100% sure the problem has disappeared (cooler weather may have affected it), but it does seem pretty much gone. I replaced the vacuum switch solenoid and 2 of the 3 vacuum hoses for the turbo (slight difference), then the O2 sensors upon seeing in the records (back to 113,000 miles) that neither had been changed. Also, while the rear was pretty steady in the midrange, the front was stuck on 1.0 to 1.1, so it seemed shot. Mileage back up as well.
Could the lack of a working front O2 sensor have caused the computer to keep searching for the perfect mix at slight throttle?

[abscate]

Usually you get a code but any deviation from the master plan and the ECU will quickly limit boost

[blkbeauty]

I replaced my CBV without removing the turbo. The bottom bolt was the PITA. Had to get under the car to removed it. The top two weren't so bad after the air box and duct that holds the PCV Nipple. Replaced the bottom turbo vacuum hose while down under.

[John850GLT]

About that turbo..... I still get some variability at low acceleration. New mystery.

So I put a vacuum on the wastegate (yellow hose) and it held beautifully at 18 (what I randomly got sucking on the hose). But the black hose at the bottom of the solenoid (to the boost?) had nothing (the blue goes to the main air intake hose). Should that black line hold a vacuum? If yes, I guess either the hose way down there is bad, or the diaphragm is shot? What does it mean and, if the diaphragm is shot, can I run the car without destroying the turbo?

Appreciate the input, and if it is the diaphragm, well, I have a replacement, but will need more info on the job if I have to tackle that.

THANKS!

[abscate]

Okay - there are a couple of diagrams in the VRD, but the short version is

One gets pressure from the turbo itself (to drive the waste gate valve - I don't think that should hold vacuum -when the engine is off that hose waits for boost from the turbo

One hose routes the boost pressure to the waste gate - that one should hold vacuum.

One hose dumps un used boost pressure back to the air duct, pre-turbo. That one will not hold vacuum.

[John850GLT]

Thank you! Very clear. Never found any of that in searches. So, another question: if I check the boost hose at idle, will I see pressure? If so, what value? Should I test at various RPMs?
And, your description implies there is no diaphragm involved in the boost, so there is only one (at the wastegate) on the turbo.
Is that correct?

[abscate]

Ive never seen values for boost pressure vs rpm. Until the wastegate closes, I don't think you will see pressure on the hoses at all - this may only happen under load.

There is a diaphragm in the wastgate as well as the Compressor Blowoff Valve (or is it Bypass Valve?)

How old is the Turbo Control Valve? - they get tired at 100k miles.

[JRL]

I would smoke the car for leaks.
My 2000 VR had all original hoses (140K miles) until last week. I've had the same code coming up for the past couple of months.
I found three (3) vacuum lines that had cracks in them and are now replaced so we shall see.
Check your J-hose in the rear. Mine was still OK but they do break/split a lot.

These cars are old and all the lines are now failing, becoming hard as a rock and splitting, etc

[scot850]

To do the CBV on a 2000 R with the 19T turbo requires removing the turbo. But sounds like you are getting good vacuum so should be ok. In standard tune the TCV Volvo version is good for about 12-14 psi, and they tend to stick when they fail limiting boost. I think it is unlikely to be that. All the replies are pointing to the possibility of leaks. Jim mentioned the 'J' hose at the carbon canister. I just did this on a FWD 2000 V70 and the original looked ok but was split on the top out of sight.

Try running some Seafoam through the engine in your next tank of gas and give the car a long run. Might be some dirt in the system. Also run 91 octane and see if that makes a difference. 87 on these engines may cause 'pinking' due to too low an octane and certainly sounds like your description of the problem.

Lastly, when were the coil packs last replaced? My 2000 R has just developed a misfire and I'm hoping that is the issue. Won't get to that for a few weeks as it is too cold and I have my ankle in a cast for a few weeks!

Good luck!

Neil.