The Oxford English Dictionary claims the origin of �toodle-oo' is uncertain, though some people believe it may have come from the French phrase �� tout � l'heure', meaning more or less, �see you soon', as Said_khan wrote above. Certainly, it sounds very similar, but there is no certainty that that is the source. It first made an appearance in English in the early 20th century.
At first sight, 'toodle-pip' - which is obviously a variant of �toodle-oo' - seems the sort of word that P G Wodehouse's character, Bertie Wooster, for example, might have been using back in the 1920s. However, there is no written record of it anywhere prior to the late 1970s. 'Tootle-pip' appeared in 1977 and 'toodle-pip' not until 1983. The latter was part of a headline in the Standard, so that may very well be where the word - in that form - originated.