sams_on_top, You have already change spark plugs and coil. Perhaps it is just a sluggish/weak battery have it tested and there may also be a stored trouble code (lazy sensor)even if he engine light is not on. Some of the auto parts suppliers offer free battery testing and code reading like Pepboys, Nappa, Advanced auto parts,etc and some of the guys are very knowledgeable and may have seen the issue often and put you on the right track. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.