Sometimes my Volvo idles rough. As if the engine is cold even after driven for awhile. It's not all of the time just some times. I can also be driving down the highway running as smooth as silk then all of sudden my Volvo "hic ups" ??? It's has if I ran out of gas for a second. Again it's not all of the time. Here are some of the things I have done to my car. New spark plugs, new spark plug wires, removed and cleaned throttle body, new throttle body gasket, new intake manifold gasket, new flame trap and hoses, and new vacuum hoses from throttle body to charcoal canister. What can cause my problem? Any advice on repairs?

Thanks