A couple days ago I got a code P0301 while driving, I hit the gas and when I came off of it, the engine started misfiring. When I got home, I switched the places of the ignition coils for cylinder one and two and it started working fine. A few days later, the misfire came back so I switched coils for cylinders two and three and the misfire persisted. The spark plugs are fine and aren’t deposit fouled. I’ve ordered new coils to put on along with new plugs just in case, but I changed the Plenum gaskets and that hasn’t solved the problem either. When I shut off the engine, there is a loud vacuum, sucking sound coming from the middle of the engine bay. Please help me out with any advice.