Hey guys first time posting, been reading the forums for a while but seem to have a unique problem.

My 93 850 GLT has developed a rough running issue with loss of power. I have looked at the various causes and read the codes and the only consistent code i get is A2 5-1-1. i have taken it to a local independent specialist who replaced the MAF sensor and since then i have replaced various parts such as the 02 sensor, all the ignition components minus the coil (plugs, leads cap and rotor). however it still remains.
the issue can occasionally be sporadic, but will usually manifest aprox 10-15 mins after start up. the car will idle roughly followed by bogging down. I have searched for any vacuum leaks and while i found a couple their rectification didn't seem to fix the issue, i have also replace the fuel pump (died on me earlier) and replaced the fuel pump relay. I have also tried resetting the ecu multiple times but it seems to make no effect. I'm running out of ideas short of changing the ecu over, being a uni student makes this a daunting task and was hoping that anyone would have any suggestions.
one final characteristic i noticed was that the exhaust when the car was running rough would be a lot more hotter and flowing a lot more than when it was running smoothly. the other thing is that it being a early model 850 i don't have EGR or duel O2 sensors so have ruled them out, the only issue that i know of is the PCV needs to be eventually replaced along with a slow leak in the radiator, but would imagine this wouldn't be causing the issues experienced.

any suggestions would be greatly appreciated.