My 1992 es300 engine sputters. Let me explain in detail. When coasting along at about 2000 rpm (40 mph or 60 mph depending on gear) The engine will almost sputter. What happens is that once you coasting at 2000 rpm the rpms will begin to drop steadily (almost slowly) until it hits 1000 rpms and when this happens will begin to suddenly jump up to and 1500 or 1750 rpms. And it will contiune to bounce back and forward between 1000 and 1500/1750 causing the car to violently buck bacwards and forwards. Keep in mind the whole time I''m just holding by foot on the accelerator at the same exact spot. If you give just a little more gas while this is happening it will stop or if you release the gas it will stop. Outside of that it drives excellent. It will idle flawlessly with a shake or shimmer in park. Also it will do 80/90 mph at 3000 rpm or 3500 rpm like new. The problem only occurs at approx. 2000 rpms What could this be? No check engine lights and I scanned it anyway and it still gave no codes

 

1) Cracks in the air intake duct work from the box to the throttle body. (Spray some carb cleaner around the hoses and if the engine surges, you found the problem.) These engines will run absolutely terrible with the smallest vacuum leak.
2) Even though you have no codes, check the airflow meter and throttle position sensor also.

I had a similar problem and it turned out to be the airlflow meter, but it threw a code. Sounds to me you have a huge crack in the intake hose.