Engine Performance problem
2002 Subaru Outback 4 cyl All Wheel Drive Automatic 40k miles

My 2002 Outback wagon with 40k miles runs well except for accelerating from a stop. It hesitates badly and you need to be very ginger with the accelerator. The RPM seems to vary +/- about 100 while idling as well. Just had a tune-up so it shouldn't be hoses, filters, fluids, etc. Is it the coil or plugs, or what?

Any check engine light ? If not it is probably something like a vacuum leak or other problem the PCM wont pick up.Was the problem there before the tune up?