The linking R, also known as the intrusive R, is a phenomenon found in certain dialects of English, such as Estuary English and Eastern New England English, whereby an R sound is inserted to separate two words which would otherwise "run together", rather than make use of a glottal stop. For instance, "America and Asia" might be pronounced "Americar and Asia". This is a list of varieties of the English language. ... Note: This page contains phonetic information presented in the International Phonetic Alphabet (IPA) using Unicode. ... Eastern New England English (also called Boston English, New England English, or Northeastern [American] Coastal English) is a [sub-]dialect of American English generally spoken by people living in coastal Maine and New Hampshire, Eastern Massachusetts, and parts of Rhode Island. ... Rhotic consonants, or R-like sounds, are non-lateral liquids. ... The glottal stop or voiceless glottal plosive is a type of consonantal sound, used in many spoken languages. ...
Linguists call this 'intrusiver' because the 'r' was never historically part of the word.
The intrusiver is probably the result of people generalising the linking-r principle so that it fits other cases that are analogous in terms of sound.
Rather than having a rule that says Drop the 'r' in words like 'more' and 'here' anywhere except before vowels, people who use intrusiver have a new rule which says Words that end in certain vowels like 'doctor' and 'saw' need an extra 'r' before vowels.
Intrusive/r/, where an /r/ sound is inserted at a word break between two vowel sounds ("lawr and order") is not a feature of coastal SAE, as it is in many other non-rhotic accents.
The distinction between /ɔr/ and /or/, as in horse and hoarse, for and four etc., is preserved.
The distinction between /ɝr/ and /ʌr/ in furry and hurry is preserved.