You more than likely have a vacuum leak which is very common and causes the P0171 error code. Make sure you take a look at the EGR valve, there are 2 metal lines attached to the valve. One goes to the rear exhaust manifold and the other goes to the intake manifold. Take the metal line/tube off that connects the EGR valve to the intake manifold and inspect the tube for hairline cracks. This is very common and I've seen it on numerous grand prixs. Also if your still running the stock intake manifold gaskets, you might want to consider replacing them anyways being they are quite old.
