I have struggled with this one too, I first checked the fire through the plug wires with my timing light. Clip onto the wire and point the light to something dark and watch the flickering of the light idle and do it about 2K RPM'*....it should be flawless and darn near solid light.
My #3&6 (same) coil was showing intermittent flickering so I put another coil in its place and had same issue. Then I removed the ign. mod. and had it testes 4 times in a row at Oreilley'* parts store and it passed EVERY time. So tonight I am checking out the wire and spark plug.
On way home from work the SES light FINALLY come on and it was a misfire on #3 cylinder, YAY I guess that my old school method weeks ago beat the comp code to the punch TODAY I guess. (hope it'* an easy cheap fix now....)
I renewed the expensive spark plugs and the best wires the parts store sold for the 00 about 2yrs ago.
I will post what fixes my issue as soon as it'* corrected. GOOD LUCK with yours!!
OK, first I started with a used but known good plug wire and it was better, but still under 3/4 throttle or a mild load on the engine it would still buck and the PO303 code would set again (#3 cyl misfire) so I then removed the spark plug to examine it for gap and such and found a small crack!! (in picture) Luckily the parts store was still open and now the missing/ bucking issue is GONE!!!!! I took it out for a test romp and was amazed at how one half arse miss can drop performance that drastic, now the passing (55- 100 MPH) is rather exciting again. LOL