Try a good old fashioned "italian tune up". Take the car out on a highway with some moderate hills and open her up. Occassionally, slow down and shift to a lower gear, then hit the gas. Allow the engine to rev really high (I don't know about you but in my normal driving the engine never revs above 2500). Get it up over 5000 (not in the red). The up shift and drive some more. Do this several times, driving at high revs in 3-5 minute bursts, going up moderate hills, etc. I had trouble passing an emmissions test. The dealer said it was due to build up of carbon, and they wanted to do a motorvac. I did this instead and passed the inspection. Change the oil afterwards of course.