W126 High idle problem

steve beard

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Hi,
Im having problems with my 420se 1990.
I have replaced the following
Rotor arm
Distributor cap
Spark plugs
Ignition leads

I have cleaned the idle control valve and when disconnected the idle rises.
The car starts fine and when warm idles at 1100 rpm unless in drive.
I cant find any air leaks.

Any advice would be very much appreciated.
Values for the sensors would be helpful and a diagram for the vacuum pipes.
 

television

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If you pull of the egr pipe does the speed increase
 

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At 1100 rpm, I would check the idle contact switch. it sounds like its not working properly.
 

ianrandom

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Might be worth trying a different idle control valve. I just had success with my SEC by changing the OVP relay. No ABS light was on so i had ruled that out, but it turned out to be the cause.

Rob Parker at Threepointedparts is good for parts.
 

Alex Crow

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As above, idle contact switch first, then the throttle plate/airmass plate potentiometer.
Beyond that, air leaks, idle valve and ECU (possibly a standalone idle ECU, but I think on this 1990 car it is all in the KE-Jetronic module in passenger footwell), although an ECU fault would be unusual.
 

Gary Hanson

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At 1100 rpm, I would check the idle contact switch. it sounds like its not working properly.
I've got a similar problem on a volvo 940, it's intermittent, and usually only happens after a run. I replaced the idle control valve and it made no difference.
 

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I've got a similar problem on a volvo 940, it's intermittent, and usually only happens after a run. I replaced the idle control valve and it made no difference.

Sorry love to help, but we only work on Mercedes and wouldn't like to guess. :)
 
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steve beard

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Thank you for the replies,
I have looked for the idle switch but could'nt see one.
The abs light is not on and the ovp relay clicks when the ignition is turned on.
If I disconnect the egr valve it does nothing unles I suck on the pipe then the idle comes down? Is this just due to mixture?
 

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Thank you for the replies,
I have looked for the idle switch but could'nt see one.
The abs light is not on and the ovp relay clicks when the ignition is turned on.
If I disconnect the egr valve it does nothing unles I suck on the pipe then the idle comes down? Is this just due to mixture?

Definately got one, look for a 3 pin plug, bolted to the manifold, close to the idle control valve.
 
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maska

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Sorry love to help, but we only work on Mercedes and wouldn't like to guess. :)

I Think You will find, Most Volvos Of That Period , Use The Same Injection System !! We are All Here To Help !!
 
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I Think You will find, Most Volvos Of That Period , Use The Same Injection System !! We are All Here To Help !!

But on a Mercedes forum??!!! The trouble with guessing or giving the wrong information cost time and money!!!!

I like to do niether.
 

ianrandom

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Thank you for the replies,
I have looked for the idle switch but could'nt see one.
The abs light is not on and the ovp relay clicks when the ignition is turned on.
If I disconnect the egr valve it does nothing unles I suck on the pipe then the idle comes down? Is this just due to mixture?

I discounted my OVP for the same reasons, but just recently found it was the cause, so wouldn't hurt to try another just in case. Mine was a very irregular high idle though, 1100 sometimes, but all different speeds when it felt like it, and sometimes the right speed but not very often!
 

Gary Hanson

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Sorry love to help, but we only work on Mercedes and wouldn't like to guess. :)
No don't worry, I wasn't asking for solutions. I've had this happen on various cars and know how to cure it. I'd check the TPS as well for a start, and if all else fails, I'd block the airway from the idle control valve to the inlet manifold, and manually set the idle on the throttle stop screw. Slightly more complicated on v engines, but not impossible.
 

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Thats cleared that up, I thought you were asking for a solution, I know lots of manufacturers were using KE around that time but I wouldn't know specific fitments.
The trouble with fitting a manual throtle idle adjustment is that it would be lacking in several areas, cold fast idle, increased idle when a gear is selected or when any other loading is applied.
 
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Alex Crow

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As above, never ever adjust a throttle butterfly on KE to achieve idle speed - a bad idea for many reasons.
 
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steve beard

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I have checked the idle switch and it is working, idles fine when cold but slowly gets higher as it gets warmer. Sits around 1100rpm all the time unless in gear.
 

television

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Yes the OVP relays made in Austria do get bad soldered joints and can be very intermittent, the Irish versions are much better,,, the only odd thing here is the engine would not go faster as it warms up with an OVP relay,,
 

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Try looking for an air leak especialy around the injector pods.
 


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