Mass flow could do the same.
I doubt it is fuel.(Meaning fuel pump or relay)
It has to be something on the ignition side.
O2 sensor might do that as well.

 

FINALLY!!!!! I Solved the issue!!!

not being a big mechanic myself I have learn one thing.. Alaway use VOLVO parts!

I had changed some leads to a set of Drivemaster leads, according to th shop I got them from they were right for my car.

However this weekend I changed back to the original volvo leads and it all jumped back to life, no hesitation for 3 days now and I doubt I will have any! What a relief!

So I know you guys know your stuff but if you ever hear of this again on these engines (B5252f not turbo.. but I imagine goes for all) make sure they have tried only testing with the proper volvo stuff.. even my dealers missed that one.

all I can say is Fwef *mops forehead*

 

saying leads are you referring to spark plug wires?

 

Yes the HT leads from the ignition coil to distributer and from the distributer to each plug.

 

Volvo 850 need the exact right spark plug. Incorrect plugs burn out really quick. Best to buy the correct Volvo part.
typical symptoms are loss of power and missfire when hot or refusal to start until engine cools