2004 SPI 60,000 miles on engine. Suddenly started to run rough. Advanced Auto read cylinder 4 misfire code. Changed plugs - no difference. Checked spark on plug 4 and plug 1 holding plug connected to wire against engine. Saw no spark on plug #4 and good spark on plug #1. Checked with MM - plug wire #4 reads 4.5 Kohms, plug wire #3 reads 5.3 Kohms. Switched #4 ad #3 wires. Going back to Advanced auto tomorrow to clear code then see if code changes to #3 cylinder. If not, does that leave the coil unit as the problem? Is there anything else to check before buying a new coil unit?