That works out about 23mpg (@ 85ppl for unleaded) - which isn't great, but for what sort of driving? If you only do a few town/urban miles at a time then it's about right. On the other hand if you're cruising on the motorway it would be bad.
compared to what? The IS200 is no ball of fire in the performance stakes.
If you genuinely have poor performance and rubbish consumption you should consider a service, new air-filter, MAF sensor clean and ECU reset.