I felt as a new member to this forum I'd introduce myself and give a big thank you to all the members who have posted such informative threads. I really am pleased to have bought a used 1994 850 turbo sedan (170,000 miles) a couple years ago, as the brand has such a loyal and interested group of owners. I have had the normal issue of an odometer failure. It was then I discovered the wealth of information and specialized part suppliers volvo owners enjoy.
I have just recently encountered trouble with passing an emissions test here in Albuquerque, NM due to visible smoke at high revs. After searching out threads with similar issues I have just received my new PCV system that I plan to install this weekend. I'm crossing my fingers that this, a possible seafoam treatment through the vacuum tree and an oil change will solve this issue. If not, it looks like I could be in for a turbo rebuild or valve seal replacement job, neither of which I would enjoy. When I do the PCV repair I will be checking spark plug condition as well as performing a compression test to hopefully eliminate the possibility of having redo the head. I will keep you updated on my progress and pass along any valuable tips I run across. Thank you, all once again for keeping older beloved volvos on the road!

 

The O2 Sensor has ALOT to do with the emission control on older vehicles as well as newer models.. maybe see if you have an old sensor or a defective one. That could be a help.
Good luck to you mate!
Direct link to helpful image below! https://i.imgur.com/zp8qsNa.jpg