I had the same problem eairler this year and it indeed was an intake manifold gasket leak. You mentioned you used carb cleaner to check for the leak. Many of the new product are not flammable. make sure you read the label and use something (WD 40 type product) that says " Highly flammable" If engine speed picks up when you spray the joint you have found the leak. I know Gumout brand carb cleaner is not flammable. Read the can. That is how I found my leak.
Gael
