If I would know the clear and encoded versions of a string could I somehow find the password and.or iv that wore used to encode it?
Encoding done with open_ssl aes-128-cbc.
What you describe would be a known-plaintext attack. Wikipedia claims that
(but that some block ciphers may be affected by chosen plaintext attacks).
Usually the IV is known, and encoded with the message. It is not secret (it is an IV, not a key).
If the encryption system is any good, there is no (known) way to recover the key from the knowledge of everything else (plaintext, ciphertext, IV) which would be faster than trying all possible keys until a match is found (this is exhaustive search, colloquially known as brute force). If the key is large enough (i.e. more than about 80 bits or so), this is infeasible with existing technology and energy (see this answer for details). Each additional key bit doubles the attacker's effort, so a 128-bit key is very far from being attackable, even with tomorrow's technology.
This property shall be maintained (then again, if the algorithm is good) even if the attacker can obtain billions of plaintext/ciphertext pairs, even if he gets to choose the plaintext (chosen plaintext attack) or even the ciphertext (chosen ciphertext attack, i.e. attack on a decrypting box).
To the best of our knowledge, AES is good and OpenSSL uses it properly.