Volvo: volvo 960 hesitation/ poor acceleration, throttle position sensor, mass airflow sensor

Question
I have a 1992 volvo 965 with 117000 miles.  I had the MASS AIRFLOW sensor changed 5 months ago by the mechanic after poor acceleration problems. It ran OK for a month and then the catalyst convertor went south and the mechanic removed the ceramic convertor. It ran Ok for another month and then started hesitating.  The error code showed 2-1-2 and 2-3-2.  I replaced the 3 wire Bosch sensor and I deleted the error codes.  It reads 1-1-1 now, but I am still having hesitation and poor acceleration especially going uphill. The fuel filter was replaced 6 months ago. Is it a defective MAF sensor, is it the throttle position sensor, is it the fuel pump?Is it the fuel injectors? Would appreciate any help. Thanks

Answer
Steve,
Check for vacuum leaks. Replace the plugs if they are older, make sure that the wires to the coils are good and tight without any breaks. If there is still problems take a compression test and see if maybe the engine is old and tired. Test the fuel pressure see that it is steady and not dropping below spec (42 psi). Continue testing the injectors, one by one unplug and see if that cylinder is the one that is not firing or weak. Injectors can be cleaned and or replaced.