Q: My car is a 2007 Subaru Forester: it is shaking when stopped & driving, check engine on, and sometimes little acceleration

Inasmuch as the check engine light is on, trouble codes will have been stored. Those stored troubles codes, which the mechanic can download, will give a good general indication of where the problem lies but a more specific diagnostic must then be performed to narrow it down. If your case is like most cases, though, the cause is probably mundane and could be as simple as a malfunctioning sensor or even merely a bad electrical connection to a critical sensor. Other possible causes of the rough operation you describe are contaminated gasoline, dirty or malfunctioning fuel injectors, vacuum leaks, incorrectly installed or damaged spark plugs, a defective or clogged fuel pump or fuel filter, failing electrical components such as the ignition control module, plug wires, coils, and spark plugs, a defective airflow sensor, dirty oxygen sensors and other causes. I would recommend that you request a rough operation/rough idle diagnostic and the responding certified mechanic will perform the required diagnostic steps, right at your location, to get this resolved. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.