If X-ray shows abdominal aorta (enlarged) does that mean plaque problem?

It might. Typically an enlarged aorta is due to an anuerysm. The anueysm may or may not contain cholesterol plaque. Aortic aneurysms are repaired once they reach a certain size due to the risk of rupture. People with aortic anuerysms should follow up routinely with a vascular specialist for ongoing management of the condition (cardiologist or vascular surgeon).