I was gifted with a 1984 380SE. it is a one owner ( I believe he ordered the car the way he wanted it)CA car. It did spend 3 years in Spain, 92-95. It has been serviced at either a MB dealership or a MB shop from new to when they stopped driving it every day in 2003. it was last smogged in 2001(from DMV records on S/N). It has not been driven since 2003 when they got another vehicle. So it has mostly sat in the driveway. It had a new battery in 2002, and new tires sometime after that, (no miles, but set so long on them that they are flat spotted).

Sometimes it starts right up and runs at 1000 rpm in Park. Other times(hot or cold day) it will not idle at all. Those times I have to start it like it's flooded(it isn't). Other times it'll idle at 1000 or just above and then drop to 800-900 in Park. I put it in Reverse and if it is still runniung, it does fine as it will in Drive. Idrive it to town(2 miles or more and return and it idles at 1000 or just over at stop signs, or it dies completely. If it stays running when I get it home and into Park it'll run up to 2000 rpm. Sometimes , if I let it run then it'll drop down to 1000 and then shoot back up to 2000, then drop and it'll do this roller coaster idle as long as I let it run.
Sometimes when I just start it up it does the run up drop back thing, but if it drops back to 500 it dies.

I took it out this afternoon, and it did all of the above, but never got much above 85 C(maybe 90C). It is not running hot. I drove about 30 miles today and when I pulled into my yard and stopped it run up to the 2000 mark and stayed there. I let it run some and this time it didn't drop in rpm so I shut it down. I let it set for a few minutes and started it up and it ran up to 1000 and stayed there with no fluctuation in rpm.

I have put injector cleaner in the gas(it was full when I got the car, and I have driven 1/4 tank of gas out of it. I filled it up this afternoon and added the cleaner, then went on the 30 mile drive.

I'm sure that the sitting idle is at the root of my problems. I intend to replace all fluids soon, but the coolant is a good color and the oil is also and doesn't smell of gasoline. Oil is clean. Car was serviced shortly before they quit driving it and maybe later as they were going to start driving it again.
They decided to buy a new car and gave this one to me.