92 Accord EX, 4 cyl, 262k miles. Between one drive and the next, the engine runs very rough under 1500 rpm in park. Does not sound like its missing, just kind of puttering/shaking. Anything above that rpm in park and the engine runs very smooth. When driving it will accelerate but runs rough at any rpm. Either a vacuum or fuel filter problem? All vacuum hoses appear intact. The valve cover does have a small oil leak.