Sounds to me like a dirty MAF sensor. I had this issue about a year ago. CRC make a MAF sensor cleaner. @ screws to remove it, and a good spray with the cleaner should see you right if that is the problem
soory to jump in but i was told that the is200 did not have a MAF sensor or was it you would never need to replace it
Mine is doing the sampe too.. so would be intersted if there was a MAF sensor scleaner out there then can you please link the site mate?
True enough, the 1GFE doesn't have a MAF sensor, it has a MAP sensor. The 3SGE in the Altezza has a Maf sensor though.
Maf sensor cleaner at CRC Don't know where to suggest in the UK, but most Auto accessory outlets sell it here in NZ.
And a How to can be found HERE