Idle Control Unit / Idle problem

Hello all,

Does the Idle Control unit just unbolt and unplug? It is a DIY item, isn't it?

I hate to throw parts money at a problem but it might beat throwing diagnostic money at it.

Where is the throttle closed sensor?
How does the idle air pump work and where is it? Do they get clogged or fail?

Does the Fuel Pump Relay act up as the Fuel Pump is ready to fail? What is the procedure to test Amp draw on the Fuel Pump?

Any help? This is to solve an idle problem during warm up.

Steve
'85 500SL (Euro)

[This message has been edited by Stevegman (edited 08-15-2000).]

[Alain V.]

Before you start buying parts, take the time to figure out exactly what is going on and when,, so that you can diagnose the problem.

You posted that this is an 85 euro 500sl, right? When you start it "cold" does it start right up but, run like crap, stumble and belch "black smoke" when you try to give it throttle? After it runs for a couple of minutes, does it seem to "clean up' and run OK?
If this is what it's doing, that usually indicates a problem with the "warm up (or fuel enrichment) regulator".

Orrrrrrrrrr, does it idle bad all the time cold & hot? How easily does it start? Details etc.



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Thank you Alain, for your response.

Starts right up, cold, and the idle has been good on warm up. When it hits around 85-90 C, the idle jumps between 600 RPM and 2000. Sometimes it dies coming down. The temp will go to about 95-100 C, the thermostat opens and the temp comes down to about 85-90 C again. After fully warming up it ran so quiet and smooth, I couldn't even tell that it was running (at about 600 RPM).

The other day it started idling very rough under any conditions, stumbling and slow to rev when throttle was applied. When it dies it can be hard to start, but was not before a few days ago. I have seen no black smoke or any smoke, but on the re-start it sometimes has an odd fuel-like smell. I have not run it more than 20 minutes or so to see if it goes away but it doesn't seem to go away as it did before.

A few weeks ago I lubed the throttle linkage with lithium grease and cleaned the Carb at the air cleaner intake, then the problem started to appear. I don't think they are related, but I may have done something. I know the idle control is related to many sensors. Maybe I banged a temp sensor or something on top of the motor. I don't think so but it's possible.

I have become frustrated. Any help is greatly appreciated and if there are any other questions, please ask away!

Steve
'85 500SL (Euro)

Added: I see in the service manual CD that the washer motor seems to be the ground for the air pump clutch. Is this right? Also, the Flasher seems to be the ground for the Switchover Valve Solenoid. Is this correct? My washer pump is off the vehicle and the flashers aren't working. Are these connected?


[This message has been edited by Stevegman (edited 08-16-2000).]

[Alain V.]

OK,It's not real easy to diagnose a car without having it in front of me but here are some ideas.
You said it "jumps" from 600-200rpm. Since your car is a euro version, I'm assuming that the battery is in the engine compartment and NOT in the trunk (like on USA cars)-First thing to check, Look at your battery posts.Do you have a "small wire" that is connected on the pos side post. Make sure that you don't have a problem with corrossion or breakage on the little "wire" that is connected to the pos batt cable at the post. If this wire has a bad connection, it can play havoc with the idle circuit. I have seen this on US version 126 chassis cars.
Once you have made sure that is OK, you need to be certain that the ign sys is in good working order. (the rough running you described sounds like a miss to me, so you may have more than one problem)
Have you "ohmed" the plug wires- to make sure you don't have a plug terminal or two messing with you?
Have you checked the plugs, to see "how they look" as far as how you engine is burning?
Is the dist cap & rotor ok?
I know these seem like stupid things to ask, but alot of times an itermittent problem that seems complex is actually a simple thing.
When the engine is running "warm" have you pulled the connector off the idle air valve to see if it "speeds up" and then settles back down when you re-connect?
There is a procedure for checking the idle air valve and control unit, with a volt meter ,I think (going from memory here). I can look up the test tommorrow, but it should be on your CD.
On your "added questions", I think you are correct, but don't have any of the CD info or books here at home.

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Thanks, Alain for your response and I will check the things listed. I recently had a timing chain, rails... as a precaution. The plugs were changed, but I suppose I should check them anyway. Rotor and cap look perfect. I bought new ones when I bought the car (assuming they needed replacing) but didn't even install them. I will try to find the test for the Idle Control Unit and Idle Air valve but I am all tied up for the next 2 weeks so I don't think I will be able to get to it. For now, I will hold off on just replacing the fuel pump relay until I know it's bad. I saw the CD had a test for the relay but it seems that the relay has to be installed and then I don't know how to get the leads from the meter in there.
Thanks again and I will return as shortly as possible. Didn't want to leave without responding to your post. I have to do some Biz travel on and off for the next few months. I would rather just work on the Benz!

Steve
'85 500SL (Euro)