W123 230CE 1984 induction noise and idle speed question

[ro80rob]

OK

I've had the bodywork restored on my 230CE, which is in a very nice useable condition having only covered just over 80k miles.
I've owned it for a few years now, and to be honest it's been stored for the last three, being only driven too and from the MOT station.
Since I have had it, it's had a couple of running issues that I've never got to the bottom of, so maybe someone can give me a little guidance or help. I don't know anyone who has a similar vehicle (230E or CE), near me so I can't cross check with my car.
Issue 1 is the induction noise. This is noticeable at idle. There is considerable 'sucking noise' (as in a sound like compressed air going through a pipe) at idle. I have noted that I can vary the level of this noise by adjusting the large idle speed screw located between the lip of the air cleaner and the rocker cover. Screwing it in results in less 'hiss' and a slower engine speed.
I have in fact, rightly or wrongly, adjusted the throttle mechanical stop screw to allow a little more air flow through that throttle butterfly valve to allow me to close down the screw mentioned above to reduce the 'hiss' from the screw and idle air distribution system mentioned above. I guess my question is, what is normal for this hissing (no typo) noise?
Issue 2 is the slow idle speed after a cold start. My car is fitted with the idle retard vacuum element on the distributor. When in N or P, the idle speed is judderingly slow. I should state that when in a drive selection, this idle retard is switched off and the idle speed does increase, but until the car has warmed a little, that is still a bit too slow to be happy with. The idle is fine when the engine is warmed. I note that my car has the electrically heated bi-metallic idle air bypass valve that is supposed to increase the idle speed when cold. I have swapped this valve with another and I have also tested both on the bench. They seem to work according to any guidance I can find but their effect to my idle speed seems insufficient. I recall that my old W123 280E worked fine when cold, with sufficient idle speed to always run fine when cold. I realise that the valve was water heated in that case. I should also add that I have checked the timing (some years ago now) when I first began to think about this fault and that seemed to be correct.
As a remedial action, I propose to fit a thermal switch that will disable the action of the retard function (i.e. disable the vacuum relay) until the engine has reached a temperature of 40 degrees. That should help with my N or P idle issues, but may well not be quite enough to address them fully.
Does anyone have any ideas about these couple of issues that are annoyances really, but are just making me nervous if my wife or daughter want to use the car. It needs to be reliable and these issues just make me nervous.

Cheers... Rob.

 

[190]

Is this Bosch K injection ?

In which case the large idle speed screw is the only adjustment intended for idle speed, it's basically a bypass around the throttle plate. It can be worth taking this screw out completely to clean the area inside which can accumulate oil/water condensate.

The bimetallic bypass valves are not supposed to be adjustable but they can be. There is a small screw and sealed lock nut on the top of the valve. If you look down through air inlet port on top of the valve you will see a quadrant that moves across the orifice as the valve warms up. Loosening the lock nut and screw will enable re-positioning of this quadrant to allow more air through when cold. With a bit of trial and error an improvement can be made. The way these valves are supposed to work is they open the port when cold and close as the engine warms up. The electrical heater speeds up the closure to eliminate the time lag of engine heat fully closing the valve.

As for the noise I can only suggest checking for air leaks at all the joints.

 

[ro80rob]

Is this Bosch K injection ?

In which case the large idle speed screw is the only adjustment intended for idle speed, it's basically a bypass around the throttle plate. It can be worth taking this screw out completely to clean the area inside which can accumulate oil/water condensate.

The bimetallic bypass valves are not supposed to be adjustable but they can be. There is a small screw and sealed lock nut on the top of the valve.........

As for the noise I can only suggest checking for air leaks at all the joints.

Hello 190
I see like myself you are in Cheshire.

Thanks for your reply. Yes it's a BOSCH K (CIS) system with the only enhancement being the ignition retard system. I am uncertain why that is fitted, except that it must change (reduce) the emissions when in Neutral or Park. One could even imagine that it is a sort of cheat device, which has proved popular with diesel vehicles, as it changes the emissions when the vehicle is stopped. Apparently that is important to pass an MOT CO test. My car passes the test fine. Looking at the result, it's slightly below the allowed pass mark. Maybe I will give the adjusting screw on the airflow meter the tiniest of tweeks if I can find my long Allen key.

I haven't taken the idle speed control screw fully out and looked in there. I believe there is an o-ring in there too on the screw shaft. I'll do that when I get the chance this week as my car is still at my mates garage where it's had the bodywork done.

It's some years ago now and your post has jogged my memory.
I have played with the screw on one of the bypass valves I had, opening the valve up as much as I could (as you say, looking down through the valve), but I did not see any improvement when it was re-fitted to the car. I should mention that I also renewed the rubber pipework and the 'jet' type fitting that fits into the crank rocker cover (crank case breather). I will get the car running and spray some brake/carb cleaner about to see if I get any change in idle speed.

Being an electronic engineer, I have thought of fitting a solenoid type idle control valve a little like the 190E system but only in place of the bimetallic controlled idle 'up' valve discussed. For simplicity, I would just give it 2 or 3 settings. A higher one for fully cold startup, an intermediate setting and a fully closed setting. Ideally, I should look into going for the full 190E idle control and pipework system, but that is maybe a little too much to fix the problem I have.

Cheers... Rob.

 

[grober]

Certainly sounds like an air leak Could be anywhere but one place often overlooked is the large moulded rubber duct under the fuel metering unit.