1988 Mercedes Benz 560sl

Hi,

Once the car is started on PARK, the RPM starts to rize to almost 2000. Couple of months ago, I noticed the hose which connects to the carburator was lose and out for a while!
I re-connect and fasten it well and the RPM seemed normal for an hour and then again started to rize again and it does not ideal anymore.

Do I need to lubricate or change anything?
Any suggestions?

Thanks
mason