Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 01-05-2015, 02:43 PM
Registered User
 
Join Date: Jan 2003
Location: Matthews, NC
Posts: 1,356
Idle control valve

This is probably a strange question but one I really would like to know the answer too. I would really like the answer for a 500SEL but for any CIS with electronic idle control equipped car would be great.
When the accelerator is OFF idle, what does the IAC do? Does it stay where it was when last idling? Does it open up? Does it close up?
I have built a new digital idle control unit that works great, idles at 600RPM in or out if gear, A/C on or off, when warmed up, 800RPM when cold, 700RPM for a few seconds after a warm start up to give the fuel system time to stabilize. I just don't know what to tell it to do when driving down the road. It probably doesn't make any difference but inquiring minds want to know.

PaulM

__________________
84 500 SEL (307,xxx miles)
Reply With Quote
  #2  
Old 01-06-2015, 10:02 AM
Registered User
 
Join Date: Jun 2013
Location: PNW
Posts: 242
I think it sets the idle at around 600 or so.

To make sure, connect an amp meter to one of the wires on the Idle Speed Control Valve (I separate the wires at the connector and use a clamp amp meter on one of the wires). Then you can have someone press on the accelerator slightly and see what the amperage is (mA).

Compare that with idle speed.

Note: DO NOT purchase an amp meter at an auto parts store! They still think a meter with test leads and a 10 amp maximum is plenty good! (May have been good for the model T, but not modern vehicles or measuring things around the home.)

Anyway you can get a clamp amp meter which measures AC, DC, may come with a temperature probe, and has a maximum capacity of 600 amps! All for under $80 if you shop around the internet. BE SURE it also says DC (for automotive work - AC home electrical work).

FYI - For other people reading this and going Huh??? There is an "idle" switch on the throttle valve. When your foot is off the accelerator, it tells the Idle Control Unit the engine should be at idle. Pressing slightly on the accelerator turns this switch off.
Reply With Quote
  #3  
Old 01-06-2015, 03:33 PM
Registered User
 
Join Date: Jan 2003
Location: Matthews, NC
Posts: 1,356
Thanks for the response. I don't have a working ICM to check. My idle is controlled by a home built controller using a PICAXE 14M2 processor. It uses PWM to control the ICV. I was just hoping someone had already checked the amps on one of these systems when the idle switch is open. My system works great at setting the idle speed but I don't know what it should do when it is not idling.

PaulM
__________________
84 500 SEL (307,xxx miles)
Reply With Quote
  #4  
Old 01-06-2015, 04:21 PM
Registered User
 
Join Date: Feb 2011
Location: Modesto CA
Posts: 4,075
pmc:

From reading through the descriptions in the FSM of the expected responses, and the test protocols, I've come to the following inferred conclusions:

1) The MB ICM controls current to the IAC via PWM, as does yours.
2) The current range is 0-1000mA. 0 is valve open, 1000 is valve closed.
3) At a road speed between 0-12 MPH the valve position is not clearly defined in the FSM.
4) Above 12 MPH the valve is closed to prevent "bucking" on closed throttle coast-down.
Reply With Quote
  #5  
Old 01-06-2015, 05:47 PM
Registered User
 
Join Date: Jan 2003
Location: Matthews, NC
Posts: 1,356
Frank:
Thanks That helps. Do you read it to mean that the valve is closed when the MPH is over 12, even when it is not in closed throttle coast-down or only when it IS in closed throttle coast-down? One minor problem with the above is the ICM doesn't have a speed input on my 84 500SEL. RPM is the only indication of speed. Right now, I have my ICV open when above 2000 RPM cruising. It slowly closes the valve if in coast down mode and below 1500 rpm. I have no problems with bucking doing it this way. So I guess I can close this book and worry about something else.

I have had this car for over 12 years and the last 4 or 5 months is the only time it has idled consistently.

Thanks again Frank and Elektri for the replies.

PaulM

__________________
84 500 SEL (307,xxx miles)
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 10:59 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page