-88 560 still high idle problems after "fixing" most of the related components

Hi guys,

I have been working with my high idle problem for over a year now, and are soon giving up.
When the car was purchased the idle with warm engine was approx 1600. I have done the following to try to fix it:

1. Replaced both injection vacuum tubes, and injector packings, and all other rubber tubes on top of the engine. All of them was rock hard.
2. Checked all bars and joints from gas pedal and to the fuel distributor.
3. Checked that the gas airflow sensor plate fully closes
4. Dismantled and fixed the idle control valve. Then did these tests:
     a. Ignition off. Connected 12V directly to the valve, valve is fully closing.
     b. Ignition on. Cold engine. Multimeter show 12V on the valve. Did NOT bridge the two sensors.
     c. Engine running. High idle. Unplugging the valve, idle increases even more. Connected 12V from battery to valve, engine stops immidiately.
5. Checked the idle control unit. Many bad connectors. Fixed them, but did not check transistors or other components.

Except for checking the idle control unit again, am I running out of ideas. Anyone out there with similar problems who can give me some tips?

Thanks in advance! 

Hi Erik ?,

did you check that Overvoltage protection Relay works and that you habe 12V and ground on idle ECU ?

Hi Eric,

to connect 12V to the valve is really a basic test and not meaningful. The ECU will never supply constantly +12V to the valve.

Especially if you reworked the valve it need to be adjusted to allow proper operation. Instructions how to adjust the valve can be found here . From your descripition it seems that the ECU is working (4.c. unpluginng increases the idle even more) but the valve is not correctly adjusted.

Let me explain how the ECU controls the valve:

- Signal to ECU is a puls width modulated signal (~ +12,5 V to ~ -15,5V). PWM ration is from 40% to 70% duty cycle
- To get proper measurements you should use a Multimeter with duty cycle function
- With ignition on / engine off the ECU controls the valve with 40% duty cycle (equals roughly the 12V you measured -> -15,5 V to 12,5V = 28V differential Voltage * 40% duty cycle = 11,2 V)
- With engine runnung in idle ECU increases the duty cycle as long as the target RPM (650 U/Min) or maximum duty cycle (70%) is reached
- From my experience the duty cycle should be around 68% @650 U/Min with a proper valve adjustment
- From your explanaition the valve adjustment is incorrect and the ECU reach the maximum duty cycle

What you should do:

- Verify if you measure above mentioned duty cycle with ignition on / engine off. If you measure 60% change polarisation
- With enging running in idle you shuld now see a duty cycle of ~ 70%
- Adjust the valve as described in the above mentioned article. But be careful and be patient - pull out the sleeve ony a little bit and retest.
- Idle RPM should now decrease - Repeat the adjustment until you measure abouit 68% duty cycle

Hope this helps to solve your issue.

Regards,
Ralf

P.S.: Why and how the +12,5 / -15.5V signal is generated is not easy to explain and would not exceed the scope of this thread.

Hi Ralf,

I did not read that Erik reworked the actuator. That is why I assumed that his idle ECU does not apply anything to actuator at all.

Hi Volker,

good point - wrong interpretation of "dismantling" from my side

However, if he pulls the plug and the idle speed increaases means, that the ECU is at least apply something to the valve.

@Erik,
even if the valve was not reworked, my assumptions are still valid.

Regards,
Ralf

Hi Doctor,
yes, I have replaced the protection relay with a new one.
Just checked with the guy who solded the idle control unit, he did not measure 12V and ground, am I afraid...

Hi Ralf,

thanks for your thorough explanation.
I need to check if my multimeter can measure cycles.
I was a bit unclear when writing dismantling the valve, sorry about that. What I meant was I took off the valve, I did not dismantle the valve itself. But I cleaned it, and it seems to be closing completely. Does that change anything? Can the valve be out of adjustment even if I did not take it apart?

HI Erik,

no worries about dismantling

Yes the valves are known to get sluggush over time. At least for the valves used from MY 86 onwards - a clean up does not really help. I put some of them for an hour in a ultrasonic cleaner with special cleaning fluid for carborators. Lot of dirt came out (fluid looks like espresso afterwarde and the valve shined like new). However, only little change for idle RPM. Adustment was still necessary.

As an alternative if you cant adjust yourf valve to work properly - there is an aftermarket valve available from Esen 08SKV241 . This valve is proven to have a good quality and stability and I'm using it for 3.000 Km without issues. However, even this valve needs adjustment as described, I have adjusted 60+ of them for w126 drivers in January with no reported defects, 

Good luck,
Ralf
 

Hi,

an idle rpm of 1600/min does normally hint to a non-working idle ECU. It would be good to know what on-off ratio you measure on actuator whiel engine runs in idle.

Hi, the idle was 1600 before I start doing anything. After the few repairs I mentioned in my post is the idle now approx 1100. However still far to high.
What do you mean with on-off ratio?

Hi unkonown Erik? ,

it is our common agreement to sign by 1st name so that we can address each other.

ECU controls clsoing of actuator by pulse width modulation. So it uses 12V pulses to control closing. This can be measured by an on-off ratio meter. Better multimeters can measure that.

Hi Dr-DJet,

thanks, I will look into it.

Rgds Erik

Hi Quickbiker2012. I found the new Esen ICV, item no 08SKV241, online. However, this part does not fit 560SL. You have a 560, and it does fit?

Rgds Erik

Hi Erik,

yes, it will fit. Believe that the issue is that the 560 SL was never sold in the european marked and is often not listet in the compatibility list.

However, all V8 engines with KE Jetronic (420, 500 and 560) in R107 and W126 (S-Class) have the same ICV

Regards,
Ralf

Hi Ralf,

ok, thanks a lot:)

Rgds Erik

Hi Erik,

All MOPF 8-cal cars as of 86 use the same idle actuator.

Hi Dr DJet,I pulled out the spring adjuster on the ICV, and it actually worked. The idle is now about 800 on cold engine (ambient temp ca 20degC). This is the lowest idle I ever had. I am aiming at 650, but is out of ideas. The idle is not steady, is is slowly changing in a interval of about 3 seconds.When installing the adjusted ICV, I noticed that a vacuum line is broken, see attached picture. It is four vacuum connections, and number four is broken off. Do you know what this line is for? I was blocking the hole during idle, but no change of the rpm.Thanks.Rgds Erik

Hi Erik,

these are 2 temperature switches (50 degrees). One activates the exhaust gas recirculation valve and the other one the regeneration valve that is connected to the charcoal container.
I can't tell you exactly which one is for what but if you follow the vacuum lines, you will find it out.

Hälsningar,
Lutz

Hi,
that is a thermo valve, meaning that both vacuum lines are connected at a certain temperature.

Hi Chromix,

thanks for the explanation. I will follow the lines.

Rgds Erik

Hi Dr-DJet,

ok, thanks for info.

Rgds Erik