Chris,
Remove the air scoop under the windshield (two screws on the outside to remove and 3 or 4 thru the scoop to loosen), the fresh air flap ( remove one of the hinges - 2 bolts - and slide out after disconnecting cable), and the filter screen.
Clean out all the leaves and debris in the airbox. Also ensure the 2 water drains are clear.
naj
68 280SL