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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
Hmm. Micro-switch does nothing when revving past 2500 RPM and manually pressing it! Going to have to order one as well...

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,501 Posts
Hopefully you are not actuating the throttle to test it.
As the car is idling press on the roller to see if clicks and the idle changes without moving the throttle actuator.

You can also remove the switch (but leave the electrical connection in tact) so that you can actuate the switch manually as the engine is idling.

You can also test it electrically, while the car is not running.

Lots of options prior to ordering a new part.

I thought you had already done all this testing months ago. I maybe mistaken.....
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
Hi,

I can't remember exactly, but I think last time I had a CTS code so I was testing that.

I did follow the RPM above 2500 then depress switch and engine should hunt instruction. Absolutely no change. (I used FaceTime from two Apple devices and aimed one camera at the tachometer. I could see the tach as I pressed the throttle linkage until just above 2500...

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
At idle the micro-switch is already pressed. Only above a certain RPM is the button released....

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,501 Posts
I think you are diagnosing the effects of what the ECU does when one is in high RPM's and the microswitch it depressed. There are more potential variables there.

A more direct measurement is: "does the micro-switch trip when depressed"
Have you done that simple test? Is the microswitch switching back and forth?
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
A more direct measurement is: "does the micro-switch trip when depressed"
Have you done that simple test? Is the microswitch switching back and forth?
Thank you.

I will try to remove it and test with a multimeter/ohmmeter. I did not order a micro-switch yet...


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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,501 Posts
At idle the micro-switch is already pressed. Only above a certain RPM is the button released....

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The microswitch trips back and fort between zero ohms and open, at idle by slight movements of the throttle actuator cable.
RPM's should all be ~700RPM in a working system when all this is tested.

I think the 2500RPM test is an entirely different test. Basically the system should cut off if you are above a limit (2500 to be safe) and the microswith is pressed (gas pedal released). But now you are testing more than just the micro-switch.
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
Hmmm. Tested the switch and it seems to be functioning, close to 0 Ohm pressed and OL when released. I guess I have to try to trace the wiring....
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,501 Posts
Good, you saved yourself $30 and the extra wait. Perhaps read up on H.D. explanations on how the micro-switch effects the system behavior. Just make sure that when it is depressed (Zero ohms) the idle control is resumed (IACV back to operating around 4V to 5V in closed loop fashion)
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
Hmmm.

Disconnected battery ground, waited a few minutes, and reconnected. Disabled blaring alarm. Started car, still 81.35 Hz. Pulled the IACV connection and checked voltage, 7.xx V. Idle around 1200 RPM when I checked before tinkering/taking measurements...

I remember replacing the throttle linkage for the cruise control I believe. Do you think I got the length wrong? When I tried to pull off the old one to lubricate it it bent completely out of shape. I found one on eBay from Europe, I think the UK....

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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The frequency of the diagnostic signal is 100Hz. I assume you meant duty cycle is 81.35%.

JZ>>>> Pulled the IACV connection and checked voltage, 7.xx V. Idle around 1200 RPM

Did you do this with it connected (closed loop) or disconnected (open loop)

1200 RPM is correct with disconnected.
7.xx V if was connected is a high voltage. If disconnected, I do not know how the system responds when it is in open loop. My intuition would be that the voltage would go lower as the system would try to reduce the idle rpm by making it closer to 2V, but I have never measured that.

A photo of your throttle linkage area could help in responding to your question.
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Hi, yes sorry I didn't open the circuit. My apologies. Just pulled it off slightly so I could measure. And yes, 81.35 %, not Hz! Maybe my mind got cold and I did not post well...

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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OK. Just to make sure:

The idle rpm went up to 1200 when IACV was unplugged
After you plugged back and measured the IACV voltage (in DC mode, not AC rms) it was at ~7Volts.
At this time of voltage measurement what was your rpm?
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Idle is 1200 RPM pretty much right from the start, everything connected, no air filter. (It takes maybe a second to rise, maybe half a second)...

It started around 7.5 V (the IACV, closed loop as you defined it). It ended around 7.1 V IIRC by the time I stopped measuring.

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Oh, I also capped the intake port with a brake bleeder cap while I wait for the white vacuum tube...

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Here's a picture of the linkages. I pulled what I believe is the one to the cruise control and verified it is adjusted reasonably well/it does not move anything when I connect it...


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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,501 Posts
Idle is 1200 RPM pretty much right from the start, everything connected, no air filter. (It takes maybe a second to rise, maybe half a second)...

It started around 7.5 V (the IACV, closed loop as you defined it). It ended around 7.1 V IIRC by the time I stopped measuring.

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Interesting.. So the ECU is keeping the idle rpm high intentionally for an unknown reason.
I suppose if you pull the IACV electrical connection while idling the RPM may even drop a little, as the IACV 0 volt might be slightly lower.

In any case the IACV is working as expected.
There does not seem to be an intent by the ECU to lower the idle RPM any.

I do not believe it is anything to do with your throttle plate actuators because the cause of the high rpm is the IACV control.

Your micro-switch checked out

Your coolant temp sensor checked out

Your OVP is obviously fine

Your air temp sensor checked out fine

We do not know about your Hall Effect sensor but if malfunctioning that does not normally cause idle higher than 1000rpm. I also do not know a quick way to test that.

So I'm running out of ideas....
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
Thank you for all the time you've spent.

I'm waiting for the IAT to arrive. Disconnecting the negative of the battery did not clear the duty cycle error, although from your notes most likely swapping it out will not do anything. I may have to trace wiring. I have a little suspicion that when I screw down the black plastic wire shield/channel that it opens a wire break, because when it's not screwed down sometimes I got a normal idle, for example when I started it the first time for this round of diagnostics....

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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What you can do is ask another forum member to disconnect their IAT during idling and see if it changes their idle at all?

I suspect it will not as this should only change the mixture ratio slightly and not effect idle RPM's.
But who knows, maybe the controller behaves in a strange way and is not fault tolerant.

I would do this for you except I do not have an IAT.

Anyone out there want to help JZ out?
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
I do remember when I pulled the plug on the IACV the RPM went to normal. I called FCP Euro with this info and they replaced the IACV. No change, the new one acts the same.

I don't have time right now as I need to get my son to his cello lesson at 5, but I may pull the IAT tomorrow when I get the chance. Gonna try to make a run to a local salvage yard regarding getting the older style headlights.

Thanks so much again! (I'll be back)...

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