I'm pretty sure that the use of the spoken "ia" only coincides with the construction "Eu ia fazer alguma coisa, mas enfim não fiz", i.e. when it's used as a modifying auxiliary verb.
When iria is used as a standalone conjugation of the verb ir, I'm pretty sure I wouldn't shortern it, but I'm not 100% sure.
For example, in the following sentence, it would seem strange to me to shortern "iria" to "ia"
Se eu tivesse carro, eu iria pra praia amanhã
Whereas in the following sentence, it seems more natural to me:
Eu ia dirigir pra praia, mas o carro tava quebrado então enfim eu tinha que pegar o busão, e claro que demorou pra caramba e enfim passei metade do dia esperando para os ônibus. Nossa essa empresa de ônibus é uma merda.
Is my intuition correct, that ia is used exclusively for when iria is used as an auxiliary verb, or am I wrong here? Answers in Portuguese are welcome, I've just asked in English because it takes me longer to write a question in Portuguese and I'm in a hurry.