[Biturbos4] S4 Idle issues

[mike]

Hi all
 
Car is a ’99 B5 S4 and it just started failing to idle on start-up
 
Last night, out from work, start it, it caught & then
died. Restart, same thing. Restart again but with a bit of throttle and it was back
to normal idle after a few seconds.
 
Drive 100 yds to car park exit and it was idling normally,
out of the car park, cover another 400 yds, switch off, post some letters, try
to restart and it died twice then idles normally.
 
Drive 5 miles with the occasional “take it out of gear and
see if it idles” test, all fine and no problem manoeuvring into parking space
at home.
 
Out this morning, first start, caught & then died, restart
and it’s fine.
 
Anyone got any ideas?