560SEL fast idle

[11293]

I know this has been discussed many times but I need clarification. I understand the main cause of this condition is the idle control valve just in front of the air cleaner. I may have been guilty of an error of judgment in that I purchased a second hand control valve and yet after fitting it the problem remains. I suspect the second hand unit was every bit as dead as the original one. However, before I shell out £300 for a new one, can anyone tell me if there could be any other cause of excessive idle speed? Is there any way of testing the existing unit to see if that is causing the trouble? I believe there is also a relay unit which controls the idle speed. If that is correct is it one of the units in the relay box next to the fuse box? Could that be the problem?
Any help would be appreciated.

 

[shayes]

I think you should check out the Idle Control Unit first. This is possibly underneath the Steering column and it is very difficult to see, at first. Not sure if on later cars it is elsewhere.

It is held in place on a bracket being spring loaded one side and one phillips the other. My own was just jammed in and easily dropped down.

Its about four inchs by four inches by one inch with a multi connector on the lower part.

Television kindly had a look at my faulty one after I had bought a s/h replacement. The s/h one worked fine until I had another problem - see "Coughs and splutters" thread or some other one?? Anyway, the original is working fine and Malcolm is going to breath on the s/h one for me. I suspect he could have a conveyor belt of these units in his house. (Thanks again Malcolm)
Apparantly dampness is the cause, getting into the unit.

i'll try and send you a photo - but don't hold your breath because i'm not too good at this.

 

[11293]

Many thanks Stuart. I have had some problems with water getting in to the car through a blocked drain tube so your theory may well be right. I shall investigate!

 

[shayes]

It's not necessarily water getting in, more condensation forming, in my humble opinion.

The unit has its entrance part pointing downward although some have said that water running down the Windscreen can get into the bulkhead and thence.....but I doubt this is the cause.

Drainage hole by wing blocked with leaves etc, I recall being a reason why a 230TE used to get water under the passenger front carpet.
In all three Mercs I have owned i have had to take out half the contents of a tree from the drainage holes!

Always someone breaking a car on ebay and so you should be able to get a replacement once you have the coding. Hopefully it will be a good one, but..

 

[11293]

I'll bear that in mind but I did have a big problem a while ago with water getting into the car. It must have been going on for a long time because when I did finally trace it I found a plastic bag lodged in the drain hole. How that ever got under the plastic valance I'll never know. Anyway it had done substantial damage in that a constant pool of water finally caused the bulkhead to rust through and water ended up pouring straight into the car. since the idle control unit is just where the water was coming in that could well explain the reason. Once again thanks for your input. I still haven't had a chance to investigate. Fortunately, I dont need to use the car every day so there is no great urgency.