Don't know anything about the suspension, mine was fitted with Sportline from the factory. Holds the road better that the other 300CE I used to have. About the idle speed, I was wondering if maybe the Thermostat doesn't work and the engine 'thinks' its still cold.
There are a lot of good guys on this website who could really give you some good advice.
I've had a few problems myself and was rescued. I'm sure it won't be long before they respond.