850 T-5 TPS readings/Misfire and pops out the exhaust
 

I have a 97 850wgn T-5. I am just getting it back after my ex wife had it for four years basically. She really drove the poo out of it. It used to run superior and now it lacks power and back fires out exhaust when more than 50% throttle. If you roll into it slow it starts to spool and pull then just sort of falls off and starts to lightly but noticeably stumble. If you matt it it either pulls good and pops loud through exhaust upon upshift or just sort of flattens out and never tries to build boost or anything. I only have generic OBDII capabilities for this car but did have my friends Snap-on Modis communicating with it as the Volvo it is. Every scanner that has been on the car shows 10.9% throttle position at idle and only 85% at wide open TP. I know its not right but I swapped an ECM from a 95 2.3T 850 and the car runs better but not fixed and still have 10.9% TP at idle and 85% TP at WOT. The Boost is better and more consistent but still misfiring and stumbling on the top. Last week I checked and replaced the TPS and just now swapped the ECM and still have these readings. any help? BTW reference voltage at the TPS is 5.02. Output at idle is 0.5 volts and 4.2V at WOT, what gives? Mileage wise the car is due a timing belt, I just did cap rotor wires. Plugs are NGK that I replaced a year and a half ago when the EX started complaining about how the car was running. in the last 18 months she put a wall mart battery in it and came crying to me when it failed and I put a good battery in. Lord knows how many jumpstarts and low voltage situations it has been through. Also 4 years ago I put in walbro pump and she has been running safeway gas. I should check fuel pressure. I use shell chev or tex premium only. I'm on a tight budget but would like to get on to some stage 3 turbo upgrades. If I cant sort this out I am after a V70R but I need to save up first. I love my Volvo, help it love me.