Car feeling weak and sluggish

Not enough fuel flow into the combustion chamber is one of the most common reason why car feel sluggish and weak. This is usually related to fuel system failure such as 

1. Clogged fuel injectors
2. Weak fuel injectors
3. Weak fuel pump
4. Clogged fuel pump filters
5. Clogged fuel filters
6. Clogged fuel line
7. Clogged charcoal canister
8. Faulty fuel pump

Another reason is not enough air flow which cause by

1. Clogged air filter

The 3rd reasons are

1. Bad / faulty spark plugs
2. Bad / faulty spark plugs wiring
3. Bad / faulty ignition coils
4. Bad / faulty spark plug cables

There are fundamental factors in combustions which is fuel, air (oxygen), fire (spark plugs). If any of these are faulty or worn out it will affect the car performance.