hi, i have a 2006 impreza 2.0 r engine . i bought the car from the previous owner in may 2015. for 1 month the car worked well. as soon as you touch the gas pedal it will shoot off, acceleration great and top speed about 190 km. as soon as i changed the rim and tyres it died. it had 16's and i put 17's, but the manual said i can make that change. it started to flat spot bad and go dead. it will crawl up small hills gas pedal to board. on flat roads as well, flat spot, dead, no acceleration. then suddenly it will take off again with a spurt but will soon die down again. on the highway 3rd and 4th gears no problems. it will fly. but it never worked again as it did the first month.i have tried to reset the ecu, but it will work better just for about 2 days and then go back again to working horribly. i have been to 5 mechanics . they said the changing of the rims will not cause that, just coincidence. i have changed new fuel filter with regulator. also the fuel pump. we put a gauge to check the psi of the pump and it held up fine- no problems.serviced the air filter. i changed the knock sensor. i replaced the air flow sensor. i serviced the injectors and throttle body four times at different mechanics. i changed the timing belt and tension-er and pulleys - . i changed the engine and transmission oils. i changed the spark plugs. sometimes on the highway the 4th gear will take long to go in and when i try to kick down, it will not and the same gear will run. the 1st and second gear will sometimes go in with a hard buck.when i apply brakes to stop, while slowing down i can feel the hard buck from the engine or there abouts as the car comes to a stop.i scanned the car at 6 mechanics! some said many sensors are bad while some say no sensors are bad.the ignition is rattling now and it is burning excess gas. i have used premium gas, super gas, super gas with octane boost - all with same results. i went back to the dealer( company ) and they told me the scanner is showing that the timing kept retarding and they don't know why. one mechanic told me to change the computer. one said that this computer cannot be reprogrammed. another said it doesn't matter changing the computer all of the same computers wil give the same problems. one said it could be the harness. now i find that even at high speeds it is not performing as good a before. now when i step on the gas pedal to drive off from stop, there is a hesitation for about 3 seconds which many times nearly caused me to get into accidents when i try to move off with on coming cars approaching. i do not know what the hell to do again. i am frustrated and tired. do you know of anyone with this problem and they were able to fix it? do you know of this problem at all? i am really looking for some help. i will greatly appreciate it. thanks for your time again.