Hmm thinking about it I would try removing the positive crankcase ventilation breather filter. It is the grey canister sticking up out of the passenger rocker cover, it also has a hose coming out of the top. The filter can get clogged, it can be cleaned with maybe gas, or you can just get a new one and replace it.
Here is a pic of it
Don't forget to Search first then ask questions later! The loose nut behind the wheel