I had that problem when mine was boosting a little bit then dropping off, it turned out to be a cracked inter cooler pipe, just go over them all and make sure all the bolts are tight.
Item For Sale: I have a zex nitrous oxide kit for sale Item Condition & Description: Every thing is there thats need to fit to a starlet except a mini relay buy you can get one off ebay. The bottle has a few marks on it but all in good condition. The intake has recently been sprayed in high temp paint. I had the intention of fitting it to mine but had a change of mind. It is a 10lb bottle and has a little bit of nitrous left. Price: £300 no offers Pictures: Payment & Shipping Details: Shipping not available, pick up only.
Some new parts have turned up, I got some depo gauges, water temp, Oil temp, Boost gauge, Oil pressure, Fuel pressure. My new 440cc injectors turned up as well today, And some new tyres turned up Yokohama Parada Spec 2
If your wanting td04 hybrid go with tuning developments. http://www.ukstarletowners.com/topic/61708-td04-billet-hybrid-300-turbo-from-tuning-developments-dyno-graphs-added/ have a look at this