Fast idle device, 280 SE 1974

[carl888]

The fast idle device on the 280 SE appears to be kaput.  I haven't checked for an electrical signal as yet but I assume its the valve.  I see its made by Pierburg.  Anyone have a part number for it?  Can't find anything on the net about it.  Thanks for any information.  Regards, Carl.

[koan]

Don't think they are available now, the replacement is square box.

Mine clicks when 12 V is applied to the terminals so it should be easy to test with vacuum.

koan

[Big_Richard]

you can test its coil with a multimeter for continuity, all it is is an electro vacuum valve - the retard line is vented to atmosphere (thru top plug) when electrified, normally it goes straight from one bottom hose to the next. Its imperative that the hoses be in the correct orientation or the venting will not occurre and you'll get no forced advance and thus higher idle revs.

that style was discontinued long ago, they are indeed square cubes now but work in exactly the same manner, though less attractive to the eye.

It only activates when the AC compressor is activated, to keep the revs constant, or when the engine temperature exceedes 100c, (aux fan switch) also to keep the revs constant.

[peterpardy]

Carl, what color are the lines that go into it Thanks

[carl888]

Hang on, a question!

Thanks Patrick and Koan, do you mean this valve is not activated during the warm up phase?  Only with the thermo fan and A/C compressor?  It was the engine's very slow cold idle that alerted me to it.  So with a low cold idle (400 rpm) is there something else I should be looking at....surely not?  Thanks for the tips, I'll check the coil, see if there is a voltage at the connector and also the temperature switch (If necessary)

Peter, the lines are white with a red stripe.  Note, I replaced these two years ago, the originals (Clear white from memory) had gones hard and one was split causing a continual fast idle.

[TJ 450]

On a K-Jet system, I believe the thermo-vacuum switch is responsible for a sudden drop in idle speed a few minutes after startup. This may also be applicable to D-Jet.

Not that I'm suggesting that there is a problem here, but it might also be worth double checking that the vacuum lines are set up correctly and that the ignition timing is within spec and that the idle bypass screw is adjusted correctly.

Tim

[Big_Richard]

cold engine auxillery metered air is provided by the auxillery air valve.

that electronic vacuum valve is not used for warming up the engine or increasing the engine revs when cold. Its only used to increase revs when the compressor clutch is active, and when engine temp exceeds 100c.

[carl888]

Patrick, my car is D-Jet, no auxiallary air valve.  Or if it does, I can't find it!


Regards,

Carl.

[Big_Richard]

i have a new computer - I'm EPC'less at the moment, i can be of no further use

but i suspect it most definitely has got one...

[oscar]

It peeves me that no manuals I've found have the d-jet m110 in detail as the m116/7 manual.  Section 7.4 is missing on the online manual and the official North American printed manual.  The haynes 280 manual puts it in the too hard basket by saying see a specialist.

Anyway, Carl, I could be wrong (I don't reckon I am ), but at idle and with throttle closed there has to be a regulated idle air bypass circuit for your car.  This would include an AAV plus plumbing that starts post filter/but pre throttle and re-enters the plenum post throttle.  Looking back through some of your pics and referring to the ones below, I have a hunch the AAV is located on the block underneath the opening of the 2nd cylinder's intake port.  That's where it is in k-jets but track the following highlighted hoses.

"A" and "B" are both post filter/pre throttle.  One of them I reckon goes to the AAV and the other maybe to where the idle screw is located.  "C" I'm convinced is where the idle air bypass via the AAV re-enters the plenum.  If the AAv is where I think it is you might need to get under the car to view it.

[carl888]

Tim and Patrick,

Thanks for the info.....Tim, yes, all set up correctly re: ignition, vacuum lines, idle, mixture etc.  Patrick, you are completely correct of course, thank you, which brings me to Oscars post:

Had a poke around the engine yesterday and I think I have worked it out.


Air, post air cleaner is drawn from this line (1), through the cold idle device and into the intake plenum via port (2):  (The line on the other side of (1) is a breather).




The cold idle device is under cylinder #2 on the LH side of the block:



Interesting that this device I cannot see mentioned at all in the M110 manual, either part one or two.  So I suppose my next step is to remove it and check its operation.  When I set the car up after all this work, it was difficult to get the car to idle at 800 rpm, the air bypass valve is nearly fully closed, so I am wondering if this cold idle valve is actually stuck open?  There are no electrical connections to it, I suppose it contains a bi-metallic coil that just relies on the heat of the block to close.  Thanks for all your help guys, looks like the work on this car is not over just yet!

Regards,

Carl.

[Big_Richard]

the K-jet versions have a bulb at the base which is submerged in engine coolant, so theres also a gasket to worry about. I suspect this version may be similar, so you might be doing a coolant drain

[carl888]

Oh great, thanks Patrick.  I wonder why there is nothing in the WSM about this?

[Big_Richard]

It's probably a component thats designed to last the life of the vehicle.

If someone hasnt already done it by the time i get home, ill supply you with a part number for a new one.

[oscar]

Glad you found it Carl.  My take on section 7.4 missing from the WSM is that everyone's English version WSMs are usually printed in NA and perhaps d-jet m110s weren't sold there or the d-jet section was only available in another format like microfiche or in German. 

The WSM for the M116/7s does have that section which says that the supplementary air valve (auxilalry air valve, air slide, air bypass valve) should be completely closed at 70degC at which point no suction should be present at it's inlet.   You can imagine then how idle adjustment becomes problematic when these things are slow to respond or don't close completely.   Other times when the coolant becomes just that bit hotter during spirited drives or city driving on a hot summer's day, you might find the AAV does actually close and idling may induce a stall since the idle screw will have been previously adjusted too far down after compensating for a partially open AAV at lower ambient temps.

If you can get a new one, do so.  They can be hard to come by for V8's, D and K jet, but hopefully you'll be able to track one down.  If you can't, try soaking it in penetrant oil or carb cleaner with a boiling water and iced water nearby.  Put the unit through a number heating and cooling cycles.  I've had some success with the 350 but still can't get it to close fully.  You've got a low mileage car but based on age it's worth revamping the AAV or replacing it.