Maybe fuel pump buzzing (will do that when really hot). As far as water ???? As far as idle, I take it that you checked for air leaks at vacuum lines and air intake hoses. How about throttle body and idle control valve cleaning? If air delivery is ok, then how about injector seals (good steady air and petro delivery = good steady combustion) ... have they been replaced.
I've hit on the inexpensive fixes first that are common issues and easy to fix.
Go from there, and as always, check the FAQ.
Gary
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