Idle too fast.

1971 merc 250ce. Finally got the car running reasonably smoothly. Issue is idle sitting at 1500 recs even when warm. Have moved throttle switch back until it starts hunting but doesn't slow down, air idle screw has little effect. Is there a base setting for the throttle plate, as in an air gap between plate and body.

Hi Unknown,

check you AAV whether it closes.

AAV??

Should throttle plate be totally closed on idle or should there be a slight gap between plate and housing.?

Hi (Steve?)

We usually sign off using our name as this makes our interaction more friendly and inclusive.

The AAV is the auxiliary air valve that sits in connection with the intake manifold. It is described in depth in chapter 9 in Volkers Compendium -  jetronic.org/en/d-jetronic/aav . In order to check whether it works as it should, you can take it off and look inside. In a cold state (ambient temp) it should be open. By putting the lower wax element in hot water apprx. 80 C, the piston in the valve should gradually move and eventually close completely. If it does not move, either the piston is stuck in the bore or the wax element is no longer working. Both things can be serviced, but only with great deal of vigilance and with the risk that the housing and internal parts will break. It is made of aluminum and over 50 years old. 

The idle run contact or the adjusting the flap is also described in Volker's Compendium chapter 12.2 -  jetronic.org/index.php/en/d-jetronic/71-...ance#Leerlaufkontakt

Best, Peter