Check for a vacuum leak. If you have a hand-held propane torch, start the engine and bleed a little raw propane all around the intake manifold and all vacuum hoses and fittings. When the engine smooths out and accelerates, you have found your leak. The engine fan should disperse the unburned propane enough to keep you from blowing yourself into the middle of next week. You didn't care much for your beard and eyebrows anyway, right?

If you don't have a propane torch, you can use any flammable liquid in an aerosol can with a tube to direct it toward the potential leak. Remember that chlorinated solvents, like brake and carb cleaner, are not particularly flammable, so they don't work too well, but they are safer to use.

If it turns out to be the intake manifold gasket (common problem), this is an easy R&R if your car is normally aspirated (not turbo).