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 Strange idle problem 
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Joined: October 22nd, 2014, 10:59 pm
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Location: South-Limburg
Post Strange idle problem
I was at a friend that had a problem with his 2cv6. The engine was running very bad idle shaking like an idiot. The engine didn't react on the mixture skrew also there was little reaction on the idle speed screw. I assumed that the level in the floatchamber was not ok. So i took the carb apart, cleaned the jets and adjusted the float level that was way of. Now the car idles reasonably well but it has strange thing. If you rev it up and release the throttle it revs down but not to idle. After that it's goes very slowly to idle. The throttle flap goes back imediatly so that isn't sticky. Other strange thing if i hold my hand on the airfilter inlet there is no change in engine speed. But if i open the oil filler the engine speed drops down??? What problem do i have?? Can a broken oilfiller have this effect on the engine speed???


March 30th, 2021, 8:03 pm
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Joined: March 21st, 2013, 12:04 am
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Location: Exeter, Devon
Post Re: Strange idle problem
My pet hate is carbs ..... :)

Common faults are ( from memory) .....

Carb nuts loose. Or, other air leak.

Second venturi not closing properly.

Choke pull off diaphragm perforated.

air bleed loose, or missing ...

Blocked fuel supply.

...... I still hate carbs ......

Also

Don't forget valve clearances

Ignition system

Did I mention, I hate carbs ........

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March 30th, 2021, 10:09 pm
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Joined: February 17th, 2009, 8:43 pm
Posts: 556
Location: NOrWAY
Post Re: Strange idle problem
RogerV, if you had been struggling with an old car from the 70's with injection, you might change your opinion about carbs. Suddenly a carb can seem both cheap and simple ;)

But yeah, an engine runs better with injection.

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Vennlig hilsen, Eirik
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Five 2CV's, DS 21 ieh Pallas -70, DS 23 h Pallas -75, CX 25 GTi automatic -89, XM 2,0i -90
And a Heinemann Z412 -80


March 30th, 2021, 10:23 pm
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Joined: March 21st, 2013, 12:04 am
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Location: Exeter, Devon
Post Re: Strange idle problem
It's not about carb v injection! :)

I just never understood them for a very long time .I think the hate me as well .... :lol:

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If you can't fix it with a hammer, it's probably electrical (or, an electric fuel pump!) ....


March 30th, 2021, 10:54 pm
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Joined: February 17th, 2009, 8:43 pm
Posts: 556
Location: NOrWAY
Post Re: Strange idle problem
Sometimes, I think cars hate me.
But since love makes blind, I keep at it :lol:

Sorry for de-railing the thread. Let's not go Facebook style.

AZL57, I think I would have tried a different carburetor, if one could be found. Assuming the rest of the engine is serviced and okay. It's quick to try a different one on. I've had troubles before with carburetors. Totally dismantled, cleaned, mounted with new parts and adjusted. Just to have no success. Engine didn't run nicely. After checking everything else on he engine, I did the same on a second used carb I had laying around. The car drove perfect. Could not feel or see any difference in wear and tear on the two spare carbs, but there you go...
They are tricky.

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Vennlig hilsen, Eirik
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Five 2CV's, DS 21 ieh Pallas -70, DS 23 h Pallas -75, CX 25 GTi automatic -89, XM 2,0i -90
And a Heinemann Z412 -80


March 31st, 2021, 1:36 am
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Joined: October 22nd, 2014, 10:59 pm
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Location: South-Limburg
Post Re: Strange idle problem
Engine runs well, there is almost no oil in the airfilter. But i heard a hissing sound sometimes. So there must be a leak? We still have to look if there is maybe a crack in the bottom of the plastic airfilter housing? But the strange thing for me is the drop off of idle speed on opening the oil filler cap.


March 31st, 2021, 5:34 pm
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Joined: March 21st, 2013, 12:04 am
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Location: Exeter, Devon
Post Re: Strange idle problem
Only thing I can think of is the air filter is perhaps blocked a little.

Does it drop just as much if you remove the air filter

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If you can't fix it with a hammer, it's probably electrical (or, an electric fuel pump!) ....


March 31st, 2021, 6:55 pm
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Joined: August 8th, 2012, 11:00 am
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Location: Korpilahti, Finland
Post Re: Strange idle problem
Air leak on manifold. If the manifold isn't removed for a while, there is one more possible leak -bolts on cylinder head. And if the manifold and one or both heads was removed, then the orientation of heads makes the issue...

All symptoms told, are air leak -related. So check everything what may be the reason...



About 70's EFI. Those are marvellous, when they are working well, but finding reason for any misbehaving, can be very challenging. Some years ago, we had some wrestling with DS 21 IE, of course with hydraulic gearbox, it took some three years before it worked well. The car, was standed on field, about 30 years. Same place all the time, and last couple decades on the ground, so when the car was moved to friends garage, the floor pan was left to ground. Or that was left there, it only needed one piece to floors, the part between left and right sill...

That project was the first Citroen of that friend, and he managed to repair everything (body, interior, electrics, hydraulics, engine, gearbox, practically all) but the IE. That was the learning session to me, to understand the D-Jetronic enough to diagnose and repair it. And at last, the engine was running perfect, after repairing fuel piping, wiring, "ECU", some sensors, new fuel pump and injectors etc. And yes, it was very challenging, and also very pleasing. Learned a lot of those EFI, and it is very robust, when working correct, and still going strong after 50 years age...


March 31st, 2021, 8:14 pm
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Joined: February 22nd, 2012, 10:34 am
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Location: Greece
Post Re: Strange idle problem
What is your crankcase negative pressure?

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March 31st, 2021, 9:08 pm
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Joined: October 22nd, 2014, 10:59 pm
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Post Re: Strange idle problem
Haven't tested it yet. We will see.


March 31st, 2021, 10:29 pm
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