1. Poss choke sensor had a similar prob on the wifes golf , how clean is the airfilter , feel for any blocked breather pipes . 2.Could be wheel balancing or a warped wheel . 3.Difficult one get yer head in the bay when cold to pinpoint it . 4 Poss a joint which seals when the exhaust expands 5.Poss head gasket check the dipstick for contamination . 6, Pull the pipe off going to the jets to see if it still does it, if it does check the pipe for splits . Other than that sell it on ebay with a warm engine and clean screen :rolleyes: