This past January I bought a non running 94 850, I suspected the oil seperator issue and bought the car for $500, another $175 for Genuine Volvo parts(from a dealership) and I have a beautiful looking and running machine. New timming belt,cleaned everything, oil seperator, intake gasket, Cam seals, EGRcleaning/gasket, MAF etc. I pulled some codes after getting it running, but they were caused by replacing a dead battery before completing all the work. My speedo is dead, so I cleared the codes to get the actual mileage(165,XXX). I have no check engine light, it doesn't appear to happen when cold (the temp gauge is always at 9:00), or under load..... just cruising along and start losing speed...give it some gas and nothing.... no dash lights either until I'm at about 10MPH.....Whatcha think?

 

Have you checked all your vacuum lines?

 

Yes, when reassembling, I replaced all vacuum lines that were loose at their fittings and secured all with very small zip ties; 2 on each end of the rubber. as far as checking after this problem developed no, its starts immediately, idles perfectly at about 850 RPM's, and otherwise runs and drives perfect, so I don't think its vacuum, I have a 91 244 that would cut out the same way a few years ago and would not restart, that was a bad relay combined with a nonworking transfer (intank) pump, and I replaced all on that car...in tank pump, fuel filter, check valve and main pump. I've got a stack of reciepts from the P.O. and don't see a fuel filter, but this car starst after a few seconds, is that a symptom of a bad fuel filter? Also, there have been times where it cuts out at say 45MPH and comes back to full power after 5 seconds or so.

 

My guess would be a bad fuel pump relay or bad fuel pump. I'd start at the relay.