1987 420 SEL Idling fast at 2200rpm.

G'day all, I have a 1987 Mercedes 420 SEL that's suddenly started to Idling fast at 2200rpm as if the automatic Choke was stuck on..
I removed the air-cleaner and sprayed all the linkages and checked that the solenoid was working correctly. Has any one had this problem before and can offer any remedies. I've had this limo since new and it has been very faithful to me. Hoping someone can assist in keeping the old girl going :)
Regards ..Stephen
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