1. If your car suffering unstable idling, weak acceleration, engine RPM and car speed is hard to raise, it might be the exhaust system faulty, suggest to diagnose at workshop.
2. If the engine forced down shift frequently, it might be the exhaust system is clogged. The clogged exhaust causing the engine power output dropped and the driver have to press the gas pedal deeper to make the car produce more power, this act make the throttle body wide open hence the ECU force the transmission downshift based on the opening position of the throttle body.
3. If minor backfire occur when engine experiecing a sudden acceleration, it might be the exhaust system is faulty too. When the engine do not have a smooth exhaustion, part of the exhaust gas will stay in the cylinder making the air mixture become lean and burning slow. When the intake valve open, the air mixture is still burning hence it will flow back into the intake manifold via the opened intake valve which resulting in backfire.
4. If "plak plak" sound can be heard from engine when sudden press or depress the gas pedal, likely it is the symptom of a broken catalytic converter. A broken catalytic converter will make the engine exhaust clogged easily.
Suggest to perform diagnose at work shop, usually the keypoints of diagnose are:
1. Check if there is damage or crack on the exhaust manifold.
2. Check the exhuast pipe and catalytic converter if it is leaking or damaged.
3. Check the silencer if it is leaking or damaged.
4. Check if there is leakage occur at the gasket between silencer and exhaust pipe, is there any damage at the exhaust pipe and silencer rubber holder washer.
5. Tighten the connecting bolt between engine, exhaust pipe and silencer.