If you have an older rice burner, and are having idle problems. Before getting too involved with the problem check the air duct from the air cleaner to the throttle body.It will usually be worse when put in gear. This is caused by the flex of the engine opening the gap. The hole is usually on the bottom of the tube and it is difficult to find at times. Running your hand over the tube may help or it may have to be removed. It may have to removed to repair it anyway. Duct tape is not a good choice as it will not hold to the material if you also use some contact cement it will stand up better. New ducts are not that expensive and I have usually found a good used one. Other causes are a dirty Idle Air Control, Dirty throttle body if you have to remove the duct I would clean the throttle body as a part of maintaince. More on cleaning the throttle body later. On some models there is also a problem with several filters. A severe vacuum leak can also be the cause but it has to quite large as usually this would increase the idle.