Unfortunately, more information is still needed.
You say that the engine decreases speed and RPMs increase. Do you mean the auto's speed decreases? RPMs indicates the speed of the engine, and as you know, the speedomoter indicates the speed of the auto. So, unless there are problems with the RPM gauge (which is possible, but not likely) the engine is actually increasing in speed.
However, with the limited information it does sound like it could be an exhaust flow problem. You might start by inspecting the exhaust system. Is there rust visible, or holes? It can be on the inside, and not visible. Besides the muffler failing, it could also be the catalytic converter.
Thursday, July 12th, 2007 AT 9:54 AM