As QinteQ and bignev says, this is such a common one. IOD is 'always' (I say that carefully!) the biggest idle draw. Why is that? Because it powers all the idle equipment in the vehicle waiting for a wake-up (From keyfob remote. Radio/accessories, etc) so when you found that the higher draw, what current was it pulling at idle? The current will answer your question. Many amps and you have a problem, otherwise I'm with QinteQ, battery would be my first port of call knowing how much trouble we all have with keeping out batteries topped up and happy (Even after buttonmod a top up from a charger now and again never hurts)