Idle controls, nomenclature, diagnostics and CD's

[DJTonner]

My '90 190E presents unusual idle behavior once it warms up. It starts and idles perfectly from cold at 700 RPM, but as it warms up, the idle speed starts "rolling" up and down – eventually swinging from 1200 rpm to near-stall. If I move the guide lever (at the end of the throttle cable) just enough to dis-engage the idle microswitch and before the throttle lever starts to move, the idle settles into a steady purr at 650 rpm.
Driveability is excellent with no hesitation or flat spots.
What does the idle microswitch do? My Haynes manual is very vague on its purpose and the “typical” engine management system wiring diagram doesn’t seem to include it.
The car spent 5 years in the United Arab Emirates where many of the rubber parts suffered in the heat - I replaced the breather hoses and some vacuum hoses. The odometer reads 90K and I believe this may be accurate based upon the general condition of the car.
I have checked the fuse in the OVP (ok) and double checked the throttle cable adjustments according to my Haynes manual. (also ok) I have just replaced a leaking EHA valve. The idle issue was present beforehand and is still present afterwards.
The Haynes manual does not give test procedures for the rotary idle actuator. I am reluctant to speculatively replace this expensive part – especially since the problem seems to go away by disabling the idle microswitch. Can the Rotary Idle Actuator be serviced?

The air flow meter contained a lot of black “grime” and I sprayed it with a throttle body cleaner (engine running). Beyond aesthetics, I suspect there’s little benefit from this procedure - other than manufacturer profitability. I am planning to remove and properly clean the throttle body once I have new gaskets and seals in my hands. I suspect excessive deposits around the throttle valve could be a contributing factor to the “rolling” idle speed.

I am confused by the Mercedes-Benz system(s) of engine/chassis numbers and seeming duplications (triplications?) of nomenclature. C series, A series, S series, CLX, 190 E, 190D, Kompressor, WDB201024xxxxxxxx, etc. ????? Is there a cross-reference that can help me sort this out?

My car has a 9-pin diagnostic socket on the left fender near the ABS unit. Is there any way of reading fault codes without purchasing a proprietary reader for this car?
And one final question – for today -;

edited due to copyright issue...

Wonderful website; regards to all,

Dan

 

[television]

Ouch, this is long biggest cause of idle flucuating is Over voltage relay.Pin 30 is the input and pin 87 is the output and should be a steady 12 volt.

The micro switch is either the auto kick down or the change over from idle relay to main ECU.

Re the numbers they are the VIN numbers that tell what group the car belongs to. in your case it will start with 201 try and put the complete 17 figure number starting with WDB in here and you will see when it left the factory
http://www.mbclub.ru/mb/vin/

malcolm

 

[DJTonner]

Thanks for the info, Malcolm.
I am unclear on how to "check" the OVP....if I pull the relay, how can I check for steady 12 volts between pin 87 and pin 30? If the relay remains in place, how do I get at pin 87 and pin 30?

The microswitch on my car is closed by the throttle linkage when the accelerator pedal is released. I believe it triggers something in the ECU that prevents an oversupply of fuel and invokes an idle speed control system while in this mode. (IE...I believe the switch signals the Idle Speed Relay....where is this located???)
If I open the microswitch without moving the throttle valve (after the engine has warmed up and the idle speeds is "rolling" up and down) it will settle into a steady idle.
The fluctuating idle also disappears if I put the car in gear from "park".

I will check the VIN against the website you gave me.

Dan

 

[television]

To check out your rotory idle valve
Disconnect the multi plug from idle valve
The ressistance between terminal 1-2 approx 12 ohm
2-3 12 ohm

Checking fast idle, connect votl meter between B+ and terminal 16 of the control unit harness muti plug. switch on ign and select P or N, if correct the meter should show a steady battery voltage, move selector to D and there should be a voltage drop.
Checking fast idle(automatic) meter on terminal 19 of multi plug. turn on ign, and select P or N meter should read battery voltage, check that when in D there is a drop.

Aux air valve, cold engine, squeeze the air hose between the bypass valve and the inlet manifold, the engine speed should drop.
Hot engine the valve should be completely closed, squeeze the pipe and the speed should not drop more tha 50 rpm.


something for you you test out.

malcolm

 

[DJTonner]

Dear Malcolm;
Thank you for your helpful replies to my thread.
The Russian MB website gave me a great deal of information; not only about my particular car but ALL Mercedes models. The graphic outline drawings/ VIN chart helps sort out the many different MB models.

I performed the OVP relay test you described by separating the relay from its base just far enough to get my multitester probes onto the pins. I checked voltage between pin 30 (and also pin 30a) and ground. I then checked the voltage between pin 30 (or pin 30a) and each of the two #87 pins and also pin 87L. I performed the tests with the ignition off, with the ignition on and with the motor actually running. .(Total: 24 voltage checks). The readings gave battery voltage each time (slightly higher when the alternator was spinning). I have assumed this means my OVP relay should be working properly.
In another thread, I found a different test procedure. Essentially, with the relay removed and a test meter set to “diode” check, a test is run between terminal 31 (+) and terminal 30 (-). A “nominal” voltage between 0.4 and 1.5 volts means the unit is ok. (I believe a complete diode test also involves reversing the leads to confirm 0 voltage in the opposite direction.) Do you use this test as well?

My car has a Rotary Idle Valve instead of the Auxillary Air device. We have had a couple of days of steady rain and I have no garage so I haven’t done this test yet. I'll post the results.

Your “checking fast idle” procedures suggest checking the voltage between terminal 16 and “B+” (Battery positive terminal ?) in P, N and D and then, terminal 19 and “B+” in P,N and D with the ignition “on”.. You indicate there should be a drop below battery voltage in D. I need more information here.
· Is the “control harness multiplug” the ECU connector?
· Is the multiplug disconnected during the test or are the test leads applied to slightly exposed pins during partial separation of the component and the multiplug?

Warmest regards,

Dan
( Starting, cold idle and driveability remain excellent; Idle still fluctuates between 1000 rpm and >100 rpm when hot in P or N. Idle becomes normal when in “D” or as soon as the accelerator pedal is moved far enough to “open” the microswitch on the throttle linkage. My automatic kickdown switch is located under the accelerator pedal in the cabin.)

 

[television]

Dan, the electrical test re voltage are done with the plug removed, the meter goes in the end of the multi socket.

Cars with rotory do not have switch over valves from fast idle, also no adjustment possible without the dedicated equipment.

O n the aux air valve you could check out the resistance. switch on ignition and check that bettery voltage exist.
Connect an ohm meter to the two valve terminals and compare the resistance reading (40ohms at 20c)
Connect a 12volt battery supply to the air valve terminals, check that after apprx 5mins the diaphragm slit is closed.

What. makes things harder is that the car starts from cold on the cold start valve.
Hope this helps a little more.

Regards Malcolm