The ventilation box is a pain to get off with the intake manifold in place so I would remove it to gain access. The old box will clean up OK if it's not cracked. You will need to replace the intake manifold gasket ($5..put it on dry). I would also clean the throttle body while I had the intake off. Replace all the rubber hoses under the manifold. You'll need about three cans of carb cleaner. The cost to me would be about $15 and require about 4 hours labor (I'm old and slow) if I didn't have to replace the plastic box. The engine temp sensor is under the manifold (center) as is the thermal switch for the cold start injector (rear). Now is the time to replace them if they are giving any problems.