New 500SE owner

Well it had to happen...the Mercedes bug has bitten deep again and I have bought another car here in the UK, so my 1988 260E is up for sale.
The new car is a 1990 W126 500SE, in smoke silver with a mushroom leather interior and it looks great. It has 127, 000 miles but only a partial service history (which normally would put me off but the price was good and the car drove quite well.) It has an electric rear blind (working), orthopaedic seats (they seem to work but make only very, very slight difference), air con (working, quite cold and it was hot today!), electric seats (all working), and lots of other gadgets which all work.
Problems with the car are:
1) Play in the steering. Over 1 inch with the wheel straight ahead, just outside spec I believe. The car is fine in a straight line but feels odd when moving quickly to the right (especially). This is almost worrying at times since it feels as if it is going to go where it wants and not where I need it to go! I will have the steering box checked and maybe adjusted next week but suspect something else is worn as these are heavy cars and steering parts certainly will wear.
2) Misfire. A new fault. The car seemed to run well during the 120 mile journey home from where I bought it. But on restarting this evening (on a very hot day - 95F in England!) it missed for about 1 mile before smoothing out. I had a similar problem with my 260E and replacing all the injectors cured the fault. However, I think this car is in dire need of some extensive TLC rather than the normal "services" it has been subjected to, so I will replace the distributor cap, rotor arm and ignition leads as a starter and will go from there. This should eliminate a simple ignition problem. Any further misfire will require some deeper investigation. I noticed that the car achieved an idle CO reading of just 0.20 % for its safety/emission test. This seems very low - I don't have any service manuals yet, so can someone confirm this is not the cause of my problem - what should the idle CO be?
3) Cruise control. Sometimes it works (like it did for 50 miles earlier today) and then it doesn't work at all. My cruise in my 124 works perfectly, so I was hoping this would too although I know they can be problematic. I expect that this could be a bad switch/bad connector/oxidation problem (well, always best to start optimistic and easy!) I have repaired a cruise control module by simply resoldering a couple of bad joints in the past and I was surprised by the poor quality soldering in the MB control unit.
Any comments, words of encouragement, advice gratefully received. I'm interested in hooking up with any W126 owners as well.
Al Bolton, G4VSQ
1990 Mercedes 500SE 127,000 miles
1988 Mercedes 260E 160,000 miles (FOR SALE!)
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Many thanks Richard, it is a beautiful car and I'm embarrassed by how many people come up to me and ask me about it, complimenting me on its condition, looks, etc!
I have the idler arm on order as it does seem to be worn, so that's a good start.
The car has a noticeable misfire as well, and I'm just about to replace the distributor cap and rotor arm to see if this helps, though I feel it's probably an injector...
-- Al Bolton, G4VSQ 1990 500SE 127,000 miles

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