Sounds like what my 260E had when I bought it. After I swapped out the EHA it was a completely different car.

SLS can be expensive if it is not working and you want it to be. Easiest way to check is to start engine and have 2 people sit in the rear (300lbs+). It should raise at this point.

A/C can be expensive if the heater core is leaking ($800 at a shop or entire day DIY as entire dash has to be gutted).

So keep the above two in mind. I wouldn't worry too much about the power problems as it doesn't sound major if the car is better when warm. A nice new set of plugs/wires/rotor/cap and EHA sound like the fix.

EDIT: That reminds me if the coolant temp sensor is broken/not functional it makes the car stumble when cold, but act perfectly fine when warm. I came upon this when I snapped mine by accident. I noticed right away the difference the next morning.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k