You can bypass a defective enrichment diaphragm or add enrichment electronically. Volvo used to offer something similar as a retrofit kit but goooooood luck finding one. These parts duplicate that system using things you can readily purchase.

A negative switching relay with time-out function:

An adjustable vacuum switch, such as the Superior K058

A spare terminal that fits the Lambda controller box. I don't have a reference on hand.

-Adjust the screw on the vacuum switch to trigger at a at a slightly at a lesser vacuum level than idle. IIRC you can hear it in-hand when the contacts switch.
-Connect the vacuum line leading to the valley, normally connected to the T at the CPR, to the vacuum switch.
-Connect a ground wire to the switch common terminal
-Wire the relay power source 12v/gnd as indicated by instructions. Adjust time-out function to approx 8 seconds
-Connect a ground wire from the switch normally open to the trigger input on the time-out relay
-Connect the relay output to terminal 11 on the lambda controller.

Drivability adjustments. Might take a few cycles due to time-limited nature of cold engine adjustments:
-Vehicle immediately hesitates when cold - lower vacuum trigger threshold and/or verify that dwell shows 80+ reading when revving
-Excessive black smoke while accelerating - decrease relay time-out to shorten enrichment period
-Starts OK but then hesitates - increase time-out to lengthen enrichment period