For some time the A2M 1647 cc engine of my Renault 18 choked every now and then when it was idling with a warm engine. It was just like it was starved of fuel for a second or 2.
Thanks to a suggestion on the Renault Classic Car Club page on facebook I found the culprit: the valve on the air intake of the air filter housing was stuck in the hot position. Thus it was running on air sucked from the manifold instead of the grill.
The valve is operated bij a small thermostat that fully opens above 26 degrees celcius. But after many years they tend to get stuck.
At first I replaced the thermostat, but the used replacement didn’t open completely. So, because I don’t drive the car in cold weather, I decided to remove the valve completely and close the hot air intake.
Easy fix, problem solved! In the video below you can see and hear the engine running before and after. First 20 seconds is before, you hear the engine choke at 3 and 10 seconds into the video. From 20 seconds you hear the smooth running engine.