I had same problem in my 1996 Lumina - it was a vacuum leak at the line to the vacuum chamber that supplies vacuum to the passenger compartment airflow positioning valves, when vacuum supply is low during acceleration, that got crushed when battery was replaced. The vacuum chamber is a hollow ball mounted inside the left front fender and the line runs right under the battery.
If you noticed this after battery replaced or any work done around the inside of left front fender, check it out. It's a lot easier than tracing the lines behind the dash.
Tuesday, October 28th, 2008 AT 8:48 PM