If you have a fairly bad idle it could be caused by a dirty Bypass air control (BAC) valve. Another way to test if your BAC is dirty or bad is to have the car idle then crank on the heat. How fast did the rpm's drop and return? or Worse yet did the car stall? If the rpm's drop a lot and take a while to return your BAC valve is not doing it's job 100%. Time to clean it out. 89 turbo one shown. Non turbo will be in a different spot.
The Black lines in and out of the bac are coolant lines that run to the throttle body. They have nothing to do with BAC valve and I have no idea why they are connected. If you remove the 2 screws holding the metal pipe the lines will part from the BAC and make things much easier. On mine however the screws would not budge so I undid the lines and let the coolant pour out into a rag; not too much comes out. The red hose underneath is normally black too and is the intake for the BAC valve. I replaced the hose in the past. It is easier to remove the pipe above the turbo and the bottom "BAC intake" hose first other wise it will be hard to get if off the BAC. If it's the original it might crack on you cause it will be rock hard. Now with the lines out the way there are two10mm nuts that hold the BAC on. After removing these unclip the the wires from it. Now tug on the BAC since it will be stuck on pretty hard by the gasket.
Now with the BAC off start spaying intake cleaner in these 3 holes till the fluid comes out fully clean. You also need to remove the leftover gasket parts from both sides.
To reinstall make sure all the gasket is off both sides and have either a new gasket or some gooey gasket maker or silicone. Remember to put the throttle cable bracket back on the top nut. If you removed the coolant lines it would probably be a good idea to replace the clamps too. I didn't and I can say that coolant leaking onto the turbo makes quite a smoke show ;)