I have a 94 Supra twin turbo 6-speed. It is basically stock, except for exhaust and a Blitz boost controller. When the car is warmed up and I'm comng to a stop, the rpm drops down to 200-300 briefly, like the engine is about to stall, and then bounces up to a normal idle level (600-700 rpm approx.). What is causing this and what is the fix? Thanks.