This one's an easy one and has probably never been touched since it left the factory. Right beside the Throttle body and cable there is a device called a dashpot. It's job is to slowly release the throttle when you let off the pedal fast. It's the same idea as the doors that close slowly so they don't slam. This device makes driving the car smother. This is shown off an 89 turbo. You have to remove the intercooler to get to it. Click HERE for intercooler removal info.
First check the dashpot to make sure it works. With the throttle cable pulled open, push on the bottom piece of the dashpot. It should move up slowly and down fast. It's basically just a little shock. To adjust it you have to loosen the 17mm nut under it. Once that is lose you screw the whole piece in or out. This changes how high the dashpot sits and therefore adjusts when the the throttle cable makes contact with it.
Now the manual tells you where to adjust it too but I just did it by driving feel. The first time I did it I made it to low and when I was upshifting the dashpot was catching the throttle too soon. This made the rpm's take a sec too long before they started to drop; making me wait a sec before I could shift each time.