2003 Honda pilot with around 250,000 miles. Been throwing a p0401 code along with random misfire code. I removed the upper intake and cleaned all of those ports, along with the lower intake port too. But the port that goes through the coolant passageway is still blocked further down than I can reach. Am I at the point where I need to drain the coolant and remove that passageway to clean it fully? Or is there another easier way?