Could be varnish and other crud in your fuel distribution system. For the cost of it - go to Pep Boys and get a bottle of fuel system cleaner and conditioner and put it in the gas tank. As you drive - at first the problems may appear more prevalent as the crud is desolved and improve as the tank is emptied. I find that highway runs helps while the cleaner is in the tank. Just a thought and a lot cheaper than other things to try. I have a 560sel that had idle problems for 2 years. If the above doesn't work - email me and I will list you the things I did to cure my problem. After much hair pulling and thinking that my V8 would never idle silky smooth - I now have success. Don't get me wrong - the idle was fine - just a slight hic every couple of seconds or so - just enough to aggrevate.