The mother tongue of all iyers is no doubt Tamil but the form of Tamil that a Kerala Iyer speaks is modified to a large extent by their constant interaction with Malayalam. Malayalam which has very large number of words owing allegiance to Sanskrit and which is endowed by the most phonetic alphabets among the Indian languages has influenced the way that a Kerala Iyer speaks and even recites Sanskrit Slokas.
The amount of mixture of Malayalam in spoken Tamil of Kerala Iyers varies from place to place. While the Tamil of Palakkad Gramams is corrupted to the extent of 20%, those in the interior of Kerala speak Tamil with a mixture of more than 80% Malayalam. It is said that people from Tamil Nadu can instantly point out a Palakkad Iyer, the moment he starts speaking. It is often said that a Palakkad Iyer prefixes most sentences with an 'Oh...'.
It is also notable that this new lingua has become a butt of joke in the Tamil cinemas. The most notable example of that would be Kamal haasan's role as a Cook from Palakkad in "Michael Madana.. ". In fact with the nasal twang added to the already soft Tamil, the Kerala Iyer lingua is really musical.