'01 Tribute V6.
I have the most confusing issues. My trib does this really weird thing that I can't figure out. When I press the accelerator about 1/4 - 1/2" - only enough to maintain speed - it bucks and shudders. If I let off the gas or put my foot into it some more, it stops doing that. It occurs more frequently when the temperature is warmer than 65-70 degrees outside. It also idles rough at stop lights, but only randomly and infrequently. I also noticed this morning that it idles a little bit irregular. Not rough, but not smooth, either. The CEL is not on and I don't have any codes.
Any ideas?

 

Could be:
dirty/clogged injectors...try some fuel system cleaner
old/clogged fuel filter... have replaced
stuck/sticky idle control arm or throttle...clean with some engine degreaser/wd-40 (external parts) or throttle body spray (inside)
dirty engine filter...replace with new
bad/failing O2 senser... would typically throw a code but any of the above items could instigate or worsen this without a code
dirty/failing MAF... would typically throw a code as well, but I think it is a Ford part and well you know how those things work (or don't)
Lastly...child's toy stuck under gas pedal....remove it (just kidding)