These had a very common problem with the injector assembly inside the intake manifold. They develop leaks around the seals at the base of the injector spider. You can remove the plenum tuning device at the top of the manifold and look in with a flashlight and see how one side of the intake is washed and wet with fuel to confirm this. To fix the problem you'll need to buy a new injector assembly and gaskets for the upper intake assembly as it has to be removed to get at the injectors.