Low idle for the first 10 miles : 1973 Citroen DS IE

Here is the situation:

- the car starts and runs fine once fully 'warmed up' ... more on that later!
- After the initial high idle on startup, the car goes to normal (lower) idle... almost 
- When the brakes are pressed or foot taken off gas, the car stalls
- i have allowed for extended warm up.. about 15 minutes 
- Car still idles low and stalls when brakes are pressed 
- After driving for about 10 milles, the cars idles fine in all situations 
- Thinking it could be the thermostat,  i replacereplaced it... no improvement 

Is this an Auxilary Air Valve (AAV) issue, or something else? 

Many thanks in advance 
Samuel 
 

Hi Samuel,

yes this sounds like an AAV issue with a very slowly operating thermostat element inside. These elements get weak over time.