Hi...

Have you looked at this page?

http://www.volvospeed.com/Repair/egr.php

I believe that there is more info at http://au.geocities.com/ozbrick850/
I can't be sure of the second one, and the site is currently unavailable.... must be a lot of Volvos in Australia... their site is often unavailable due to high usage.... :)

You should take a very careful look at all the vacuum lines and elbows. Since the unit was recently serviced, there was a reasonable amount of poking around and moving stuff. Remember that a leak in a vacuum line not directly related to the EGR, but being connected to the same vacuum source, can cause fluctuations which may effect the amout of vacuum available to the EGR diaphragm. If the EGR is the first system which doesn't operate correctly as a result of vacuum loss, that's what the computer will sense, and generate the appropriate codes. Whenever there has been recent service performed, and there are strange, inconsistant down-stream things happening, the first thing I look at are the vacuum lines and elbows.... with a bright light, and inspection mirror if necessary. Even if that's not the problem, you have eliminated one major potential source of such a difficulty, and that allows you to move forward with your troubleshooting process. Also make sure that the line from the exhaust is intact, and that the fitting is tightend properly... if it's sucking fresh air instead of exhaust gases, that might trigger your error code also. Good luck

Marty
'96 855T