Volvo D6 control lever fault

[KDee]

Hello all,
New to the forum, hope your experience can help me.
I have a D6 370 in my Grandezza 31 OC. Three times over the past two days, when starting up, I have had a warning buzzer and the message "check control lever".
Each time I have needed to re-calibrate the control lever to get the engine to start. In addition, the engine has begun to surge at modest (1200-1800) revs, no problem above 2000 rpm. Any ideas what is causing this?
Thanks....

 

[KDee]

Problem now identified (by a very expensive diagnostic call-out visit). Apparently the potentiometer in the control lever mechanism is faulty. Replacement estimated at £75 plus labour.