When standing up from a prone position my l knee made two loud popping sounds followed by immense pain, swelling 4 days later. is this an acl issue ?

Unlikely: More likely to be a meniscus tear. Would be unusual to rupture an acl without significant trauma. With pain and swelling after 4 days its time to see your doctor.

I do believe so: Most likely meniscus problem could be torn . Check it out.

No: Isolated popping like this is not necessarily abnormal. If you have persistent popping senstations, pain and swelling then consult a good local orthopaedic surgeon.

Unlikely: Unless you had a problem or injury to your acl previously , acl injury as a cause is very unlikely. Popped and severe pain followed by delayed swelling could indicate a meniscal tear or a subluxation of your patella. See an orthopedic doc. May need an MRI to confirm diagnosis