It does not sound e-. When all accessories are on the engine sees a higher load, which the computer counters with more air. It could be that the Idle bypass vavle is gummed up and sticking. When you say that you can't get the idle right what do you mean. Is it always high? Does it surge? Has the problem been getting worse over time, or did it come on suddenly after an oil change or something?
There is a proper procedure for adjusting the idle speed. The books outline a few steps which let the computer know that the set idle speed has changed. They do not recommend just turning the idle screw. I tried that procedure once. It did not seem to yeild better results than simply turning the screw, so I just turn the screw. If yu are having troubles though, it may be worth going through this process.
Good Luck.
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