Sounds like the idle set solenoid is being a bit dodgy..
Best bet if you havent done anything like this before is to get a gregories manual on your car. They arent cheap at $50 but they tell you how to service these type of things. (the fault finding sections are useless).
If you then look at all the parts which affect idle, such as the idle set solenoid, you can begin to track down the fault.
Sorry I cant be specific about your prob, but ive got a good ol carby on my car.
If you dont get any more replies, try posting your problem into the I6 (inline 6) part of these forums. More people tend to read posts there