This is a well recognized issue with these vehicles. There are two coils, each activating two cylinders/plugs. They are situated behind the plate above the cylinder head cam cover. It is secured by three or four Allen/Torx-headed bolts. It is necessary to detach the cross engine intake pipe. Upon removal of the plate, the plug leads and coils will be clearly visible. Any of the components may be defective, including the low voltage wire from the engine ECU, which often fails due to elevated temperatures from the engine. Numerous postings and images about the subject are available here; it is advantageous to peruse them.