Subaru 2004 2l auto tip tronic. It seems to hesitate or have slow or lack of power when you accelerate slowly
Just resolved a similar problem on '03 Forester 2.0 turbo. Car would not respond for 2 to 3 seconds when the accelerator pedal is pushed. Also, when it finally kicked in it lacked power. I did not take it in until check engine light came on for O2 sensor...p0171... After explaining problem to mech he said it was either the fuel pressure regulator or the fuel filter, I took the opportunity to replace spark plugs, air filter, oil, oil filter, and a very dirty fuel filter(which I believe was the culprit in my case), and of course a very expensive O2 sensor. Car drives like new again...response is super! Since the initial problem of slow acceleration did not produce a check engine light I was reluctant to mess with any of the other sensors.
What you need for proper engine operation is a) air, b) fuel & c) ignition. If the the air intake is not obstructed, the throttle plate/cable not loose or sticking, then look for spark plugs and ignition wires. If all that is sorted out, look for fuel pump issues, or sensor errors (although you did not mention a check engine light).
Most likely you need to replace the plugs, and/or the ignition wires.
I have a 2007 Outback that had the same symptoms. Taking the MAF (Mass Air Flow) Sensor out and spraying some electronic sensor cleaner on it removed the hesitation. There are just two screws that hold it in to the intake, so it is a quick operation.
Not sure if long term the MAF needs to be replaced but for now it is holding up.
I had the same problem in my 2004 Forester xt automatic. Also the engine light was on for about a half a year. The car would first hesitate a lot to accelerate and a couple a day ago did not accelerate up a hill. My local mechanic said it could be two things: the flow meter (sensor next to airfliter) or the throttle sensor. To check the flowmeter it is very easy, just disconect the plug. I did it and the car runs prefectly so I know it is the flowmeter. Also, I had a p0107 code before. If the problem is still present, it is the throttle sensor.