Good day to All MazdaSpeed Family. I have an ongoing issues with my 06 MazdaSpeed6. Little background : I travel for work allot. Hence my car will do more sitting that driving and it has little over 36k miles on it. Came back from work, started my car and took it for a drive. About an hour into driving car started stuttering and bucking at time. But then it will pick up again and work fine. Took it out for another drive the following day and it was bucking 5 minutes in... It limp its way back home. Did some checks and it was running rich. Had to leave for work again so I did not get to do much to it. Came back home did some troubleshooting and changed relief valve on the fuel rail, took apart HPFP cleaned it upgraded the rubber seals to handle Ethanol and changed the ITFP as well. I also changed the spark plugs and Coil pack with NKG. It started right up drove from driveway and it struggled to get back into the driveway. Did a compression test. Came back great. But I'm checking the plugs, 1, 2 & 4 had little build up on them but 3 looks brand new. I have done continuity test from that plug on the harness to the ECU, the relay in the engine bay, the fuse in the engine bay and also to ground....... Any other suggestions on where I can check or do to resolve this issue.