engine shudder at 100Km+ 87 Hiace

[ian123]

I just bought myself an 87 hiace to travel around australia with, its great, i love it and it seems bulletproof. however its got a debilitating engine shudder at around 100 to 110Km (once at 85) its fairly inconsistant but it often happens on hot days For example when i start it in the middle of the night, no problems, but if i start it 12 hours later in the middle of a hot day, theres almost no chance.. its petrol, 2.2, 4 cylinders with an auto choke.
If anyone has any ideas that would be great cuz im fresh out..