The torque converter controls the amount of fluid passed to the automatic transmission and allows the engine to run optimally. Signs of a faulty torque converter include slipping gears, loss of acceleration, decreased fuel economy, shuddering between 30-45 mph due to misalignment, and overheating from low fluid pressure preventing proper power transfer. A malfunctioning torque converter can also cause the transmission to take longer to engage the engine, potentially stalling it, and should be repaired immediately at an automotive shop.