intermittent fast idle getting worse
I have an 83' 500sl euro. We don't drive it much. Very little during the winter months. The weather is starting to get better and my wife took the car out. When she came back she mentioned that it seemed to be idling very fast and wouldn't slow down. I took the car out and it was fine. This was several weeks ago. We now have been experiencing this "fast idle" between 1600-1800 rpm intermittently. The car may be sitting idling fine and all of a sudden it will just kick up to 1600-1800rpm this is true also when driving, you can tell sometimes its idling normally and sometimes fast. Other than the idle the car runs great. This car used to chug just a little on startup and you had to wait 20-30 seconds and then it would run just great. I assumed this was the warm-up regulator and since we didn't drive it much this was no inconvenience. Now though with the fast idle I'm afraid we're going to damage the transmission by shifting with this fast idle. I've read some of the posts here. I've taken the idle control valve out and tried to clean it. If anything the problem has gotten worse. I 've read of the idle control unit. Does this model have one, and if so, where? Could this be warm-up regulator, idle control valve. Any thoughts would be greatly appreciated.
I'm slowing refurbishing the car, replaced most of the interior a year or so ago, so, I don't mind spending some money on the car but would prefer as much info as I can get before I start thowing money at some of these more expensive parts.
1983' SL500 euro