1800: P1800ES fuel injection

[142 Guy]

Originally Posted by VolvoRoyS

The car had no hose linking the vacuum retard to the inlet manifold (it was blanked off at the manifold), the inlet air hose was ripped apart and the air filter very dirty. So far I have fitted a new air filter, inlet air hose but when I fitted the vacuum advance hose there was a very noticeable drop in engine revs so don't why that would be.

However, idling is quite rough so now plan to focus on the fuel injection starting with the throttle valve, throttle valve switch and idle adjustment. Any suggestions as to why the idle would be rough especially when cold would be welcome.

The drop in idle speed is normal if you reconnect the vacuum retard function. At idle, increasing ignition advance from a base point tends to increase engine torque which tends to increase engine speed (up to a point). Retarding the ignition reduces torque which tends to drop engine speed. More modern cars with ECU controlled ignition timing use this characteristic to help stabilize idle speed (engine speed goes up - retard ignition slightly to bring it back down and vice versa).

If you set your static ignition timing at 10 BTDC and set idle speed with the vac retard disconnected, attaching the vacuum line will then cause the distributor to retard about 5 deg which causes the idle speed to drop. In the service manual you will find that basic ignition timing is checked with the vacuum line blocked off; but, idle speed is set with the vacuum line attached. The engine will operate satisfactorily without the vac retard connected. The retarded ignition at idle helped to control nitrous oxides by slightly reducing combustion temperatures. With the vac retard disconnected you will likely notice that at idle the exhaust has a more acrid / eye watering characteristic.

What is the nature of your idle roughness? If the engine speed is hunting at idle that is a sure sign that the throttle switch has not been set up properly. The procedure for setting the throttle stop screw, adjusting the throttle switch and setting idle speed is set out in the fuel injection trouble shooting manual. Owners frequently use the throttle stop screw to adjust idle speed which causes all kinds of problems for the D jet system.