Ok mine is an 01 4.0 sohc. I have changed the sparkplugs with autolite, wires, and today oxygen sensors. the engine only has 45,000 miles on it. OK now the problem i have, and has been doing it before the parts mentioned above. sitting still you push the pedel and hold 2 or 3,000 rpms. the engine for a second sound like a vacumme leak the tone of the engine changes then back to normal. all of this happens for about 1 to 2 seconds. The engine generally feels weak, then one day driving home from work on that perfect day and perfect temp the engine was noticably alot stronger. Anyone have any ideads, i'm lost.