Idle change overnight (no idle fluctuations)

My 1973 Citroen DS 23 IE (D-Jetronic) is running well. But one problem I am trying to resolve is that I would set idle properly according to specs (after warm up, etc...) and the car would idle fine.

Next day, or sometimes later in the same day, the idle will change by a few hundred RPM. There is no fluctuation in idle up and down as in the symptom of a bad auxiliary air valve (AAV), rather, idle is steady, but varies up or down over time, and remains steady at this particular RPM (in semi-automatic Citroens, there is a low and high idle, both go up or down by the same delta).

Could this still be an AAV issue, or? 

Any pointers will be greatly imprecated!

Samuel
  

Hi Samuel,

could well be a sticky AAV yes. And that will create big problems on DS semi-automatic if idle is not exact.

Thank you Dr DJet ... much appreciated!

I disassembled my spare AAV and will clean and test. So, far it looks like the wax thermostat cartridge is defective.

Best
Samuel
   
 

Hi Samuel,

well a defective thermo element is the normal case. It is dangerous to pull out upper part of AAV. That is fragile and aluminium cast can break easily. So be happy that you managed without breaking anything and without damage on fitting.

Is there a manual for how to dissassemble AAV.?

Hi,

of course there are good recipes on Youtube how to destroy your AAV. Some believe that it is just dirt and that they can make AAV work again by just cleaning. In reality you need to replace thermoelement including holder with press fit and sealing.

Yes we have Company here that deliver overhaul kits for AAV, my plan is to try this out one day.

BR Terje 

Hi Terje,

I have seen one company in Scandinavia that delivers a very strange thermoelement with different shape and non-specified expansion characteristics. Another company ships the thermoelement without ensuring that its actuatr does not slip out due to temperature changes. That can destroy thermoelement. Loose elements always have a slamp that prevents that.

It was this Company i ment, any exoerience?

www.aavpart.com

BR Terje

Hi Terje,

yes these guys use a different thermo element than Bosch. And they do not show  specs of that element. Original one must move from -30° to +100°C. Thermo element must keep pressure an actuator. That is why original ones have a clamp that must be fitted at all times. It prevents actuator from slipping out or sucking in air. If that happens, this element is scrap.

I bought the thermostat capsule from this guy:

www.ebay.com/itm/325893741284?mkcid=16&m...=artemis&media=EMAIL

I have not reassembled the AAV yet, but the size and markings appear to be the same as the original Bosch

Hi Samuel,

I cannot judge the rest. But have the thermoelement without clamp is a high risk. Pin must always be under pressure from a clamp. You can face easily that pin gets pushed out and element sucks in air when temperature falls again. Then it is scrap. I cannot comment on the rest as I have not seen it.

Have a look at Bosch F 026 T03 038 thermostat. It always contains this clamp.

That is the reason why I never ship my version of thermo element with holder. I do not want to take such a risk. Additionally I disagree with the methods described. I do not recommend to push in something from top - will not work with Mercedes V8 D-Jet AAV anyhow. This method is too risky to put too much pressure on thin wall of orifice and can deform it. I always use a tool to pull out old thermoelement without any risk. Then you need to ensure easy sliding of piston inside. Just ultraonic cleaning is often not good enough.

Anyhow guys it is up to you. But always remember that you will not find replacement easily if something fails

Good luck guys.

Thank you Dr-DJet for the observation and the note... Very helpful!

Samuel