Volvo: 1996 Volvo 850 Turbo, mass air flow sensor, mass air flow

Question
Hi,
I parked my car and it was running fine, then when I went to start it it hesitated, then quit. I can start it up and the fast idle works, then it kicks down and stalls. If I feather the gas careful not to induce the turbo I can get it up to high rpm and hold it there, but eventually it drops down to idle and quits. Any thoughts?

Incidentally I switched from 87 octane gas to 92 just yesterday. I purchased a code reader and it only has the misfire codes as well as a freeze code about an oxygen sensor. The code reader did not indicate that the catalyst, evaporative, oxygen sensor, or oxygen sensor heater diagnostic had been completed. Could it be the oxygen sensor, and would you recommend replacing the front or rear sensor?

Thank you so much.  

Answer
Shawn,
Clear all the codes and reset the adaption then see how it runs. If it is not good then test the fuel pressure. It should be 42 psi. See if you get any fuel trim codes or Mass air flow sensor code. If the O2 sensor was bad there would be a code to indicate that. Monitor the O2 and see if it is working and also see that the rear one also works. I would replace the front and rear sensor with sensors from the dealer. They will have the the latest ones and maybe even a small wire harness to go along with the new sensor.