So my wife was driving the car... she boosted to get around a semi on the freeway.. and then heard a pop after a few moments of strong boost. The car forced itself to down shift to zero MPH... so she pulled over on the side an I came and towed the car home. Upon inspection, I noticed that the upper intercooler pipe had popped off on the engine side... which in retrospect was my fault.. since this was the day after i replaced the radiator, and I must have not tightened it up enough... Anyway, now the car runs fine again... but the boost guage reads dead center and doesnt move. I assume theres another tube, or vaccum line that may have also popped off that would have casued this condition.... but i cant find anything.... any suggestions? Thanks!

 

My turbo boost gauge had stopped working (it was stuck dead center) and I was able to fix it by finding the vacuum hose that I had forgotten to reconnect after changing out the PCV system. The vacuum hose you are looking for comes out of the driver's side firewall (left side) and is routed towards the left front headlight. (It is a rigid black plastic hose on my 1995 850 Turbo but was a rigid off-white plastic hose on my sister's 1996 850 Turbo. The diameter is narrower than a pencil.) Then it turns toward the center of the car and goes just behind the hood clasp then over towards the throttle body / vacuum tree. I wish I had a better description for you... but that's the best I can remember. Take a look at your car and let me know if you still can't find it. Maybe I could take some digital photos and post them for you later this week. Just let me know.
Good luck!

 

I think i know just the hose... maybe.. we had one of them go brittle and break off... but we cut it and re-connected it... perhaps it cracked. it was one of two that connect one on top of the other, right on fron of the engine.... just to the left of the black plastic sheid that covers some "stuff"

 

I think you have found the correct hose! Under that black plastic shield is your throttle and a vacuum tree. The vacuum hose for the turbo gauge goes into that tree.

Mine also broke and I patched it with a piece of rubber vaccum hose. You might have another break in the line...

 

The guage on my '95 850 is not working. I followed the vac line as far as I could and it seems good. I'll keep checking.

 

Well, I finally fixed it. I looked as best I could without removing the battery but could not see any holes or breaks. I had a few holes, very large ones. Who's idea was it to run vacuum lines under the battery tray?

I pulled the battery and the tray and found that both of my lines (cruise & turbo boost) had large holes in them, the hard plastic tubing. I cut them and put a rubber vacuum line to re-connect them and now both works great. :-)