Green’s Dictionary of Slang

1. an automobile.

1899		Province (Vancouver) 19 Dec. 10/4: The Sultan of Morocco, unwilling to be behind the times [...] is creating a considerable sensation with his newly acquired ‘teuf-teuf’.
1900		Portsmouth Eve. News 10 Nov. 3/2: Four years ago motor car owners indulged their fancy for the ‘teuf-teuf’ under many difficulties.
1903		Dundee Courier 13 Oct. 4/2: The King’s ‘Teuf-Teuf.’ [...] The unreliable motor has a habit of stopping [...] when least expected.
1904		Eastbourne Gazette 10 Feb. 3/2: The rapid swish of thew wheels and the occasional sound of the motor horn — ‘Teuf! Teuf!’ — have a realistic effect.
1913		Wasau Dly Herald (WI) 31 Oct. 11/2: It appeared thata teuf-teuf was an automobile.
1918		Winnipeg Trib. (BC) 27 May 10/4: ‘Teuf-teuf!’ there goes the motor horn. Husband is staring out down the highway.
1923		Roscommon Messenger 6 Jan. 3/3: Before she’d half finished she heard the teuf-teuf of the motor at the door.
1960		Windsor Star (Ontario) 29 Nov. 20/4: In France, the old car clubs are often called ‘teuf teuf.’ Sort of French for ‘putt putt’.

2. used as phr. to signify ‘goodbye’.

1907		Hants. Advertiser 12 Oct. 6/3: Deem me not fickle, Reynard mine, / If, grown unsportsmanlike, / My errant fancy should incline / To following- the bike. / If naively I would substitute ‘Teuf-teuf’ for Tally ho!
1961		(ref. to 1919) R. Usborne Wodehouse at Work 217: In The Coming of Bill [...] Lord Tidmouth, a Knut, says good-bye in six different ways: ‘Bung-ho’, ‘Teuf-teuf’, ‘Tin-kerty-tonk’, ‘Poo-boop-a-doop’, and ‘Honk-honk’.
2001		J. Burkardt ‘Tom Tom’ Wordplay 🌐 teuf teuf (goodbye).