Actually, I think you have it backward. There are many speech delayed children who do not have an ASD, and some are just speech delays without a cause. You do not need a cause to get therapy. Go to a speech therapist, and if the issue is an expressive delay, receptive delay, or articulation disorder it does not really matter why, they treat what they see according to the evaluation data.
As for other diagnostic lables, there is apraxia, Central Audio Processing disorder, mental retardation, cleft palate...many others. You would probably know that more was wrong than a simple delay if your child had one of these. Sometimes, a speech delay may be remediated when the child is young, and other issues will come forward later, like a learning disablity, ADHD (usually without the "H") or Tourette syndrome.
All in all, it really does not matter why, the therapy is usually the same no mater the cause of the delay, and the earlier, the beter.
M.
I have said it before, and I will keep saying it, and I do not mean to step on anyones toes, but kids who will do just fine without therapy look just the same as kids who desperately need it, and the cost to a kid who needed it and did not get it is huge. Don't ever wait on development, the one who pays if you are wrong is your child. Early is best, and sometimes, it is essential. Why gamble? MR
One more edit...ECI and the school do offer free interventions, and if all you are looking for is for your son to be "functional" than this is fine, but if you want to maximize your child's potential, also get a private evaluation and seek private therapy in addition to public services. You do get what you pay for, and the only thing you really have that is free here, is time...you can't get one second of it back once it it gone. MR