2000 S80 Turbo Control Valve, any way to test?

neworion · Post by **neworion** » 10 Jun 2014, 22:45

RPM is stable at idle*, but surging a hundred RPM or so at highway speeds. The surging was almost undetectable at start - slowly worse over several months, most prevalent when the engine is warm. The turbo control valve (TCV) may be failing? Is there a way to test it? This issue was clouded by a vacuum leak, now repaired. The symptoms seem similar to a vacuum leak but I've replaced most vacuum lines and tested with gas and have found nothing.

*Until today, the idle was stable. Now there is a minor surging in the engine at idle that is too small to be reflected in the tach. This followed an increase in surging at highway speeds. Took the car to a non-Volvo mechanic and he said there were no codes. Will TCV issues throw a code? Car has 85k miles. New fuel filter, spark plugs (all clean), cleaned the mass airflow (MAF) sensor. I've read hundreds of posts trying to narrow this down and have demoted the Electronic Throttle Module (ETM) and MAF on the list. Any suggestions? Thanks!

matt5112 · Post by **matt5112** » 11 Jun 2014, 04:48

For the ETM, I'd suggest the test built into Vida.

For the MAF, unplug it when the car is off, then drive it for a day or two, see how that goes.

neworion · Post by **neworion** » 11 Jun 2014, 22:48

Thanks for your help - I followed your suggestion: unplugged MAF and drove hwy beyond where trouble usually is noticeable, made a pit stop, plugged it in, and drove back. No noticeable difference between the two. No mechanics with Volvo-specific VIDA in my rural area but will check again. Plumbing the TCV charge pressure inlet (red) directly to the wastegate bypass regulator line (yellow), would open the wastegate and taking the turbo offline altogether. If TCV is the problem the surging goes away. If it is the ETM (or other) the surging remains. See any problems with that?

Post by **Oly_850** » 12 Jun 2014, 11:51

If you apply pressure (by just blowing) in the yellow hose, you should hear the waste gates open and snap shut under spring pressure when you release. Your red / yellow combination should accomplish the same, and I'd give it a try, that would isolate the problem to the TCV or a vacuum leak in the blue line.

neworion · Post by **neworion** » 12 Jun 2014, 15:31

Thanks Oly. I'll check the wastegate actuator as you suggest. Then after warming the engine I'll connect red to yellow, plug blue line and see what happens. Here is a diagram cobbled together from some 'borrowed' images. No points for artistry, yet this seems to be how the TCV controls the wastegate actuator which in turn controls the wastegate valve. The compressor bypass valve (CBV) is shown as well. My current theory is that the solenoid in the TCV is weak, or the TCV seals are weak and leaking, or there is a vacuum leak in some line I haven't replaced yet, or... I'm really just hoping I don't have to pull and clean the ETM.

Post by **Oly_850** » 12 Jun 2014, 17:04

Cool diagram!

neworion · Post by **neworion** » 12 Jun 2014, 22:59

Thanks, Oly - I thought others might find the diagram useful and there wasn't any one diagram that tied it all together. Blowing hard in the yellow hose had no effect - the hose seemed plugged. Should that really move the wastegate? Time to replace the wastegate actuators? Hooking the red line to the yellow and plugging the blue: the car drove well - except for the surging. So it seems the surging is not turbo-related. Drove with the MAF sensor unplugged (again) to double-check and still got surging. From what I've read it seems if it were an ETM issue the surging would be prevalent at idle and there is no issue at idle. So, it could be a vacuum leak at higher RPM? I tested with gas only at idle. Will replace the short (3") vacuum lines at the turbochargers and check the air path from compressor to intercooler to ETM. Could be fuel pump or fuel pressure regulator?

neworion · Post by **neworion** » 13 Jun 2014, 08:36

There is this post that includes info on cleaning the TCV.