1989 300E, Some questions....

MB Experts- When I start the car up the white fan comes on automaticly. No AC or anything on. The black fan doesn't come on when i first start. Should the white fan only come on when the engine hits a certain temp?
2. How quiet should this engine run at idle? It seems to be running quit rough for a mercedes gas engine. My old mans 2000 E320 is as quiet as can be. When I stop at a light in drive, it thumps like a buh, buh, buh..... When the AC is on its thumps more and harder. After 10 MPH its ok. Be aware that I only put 6K miles a yr on the car and some times it sits in the garage for 2 days, rarely 4 or 5 days in a row. If anyone can diagnose the problem on here I would greatly appreciate it. Everything on my car has been serviced all the time, Mobile 1 every 5K, ect. THe car has 119K on the odom. It s been well taken care of. No coolant leaks either.... And if someone can pick out the issue, what am I lookingat for a repair price.
Rgards- Chuck
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The engine only appears to run better at higher rpms.
When was it last tuned up? Spark plugs etc?
An ignition wire or two could be marginal.
It could have a vacuum leak which allows unmetered air to dilute the air / fuel ratio; that will cause one or more cylinders to misfire, especially at idle. at hot idle listen for a hissing noise near the intake manifold. Look for a disconnected, cracked or broken vacuum hose.
Such limited use contributes to dirty fuel injectors. Add a can of Techron in the fuel
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Sounds like your motor mounts are shot.
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