300 Sl 107

[timmo]

Hi all, I have an intermittent problem with my 1986 300sl. Sometimes when I start the car the ABS light stays on and during this time the idle speed seems a bit low and lumpy....even stalls when cold.
Anyone any ideas.....When the ABS light goes off, idle speed is perfect even when cold.

Thanks in advance, Timmo.

 

[Myros]

could it be the other way around?

is the lumpy running causing the ABS to come on, say for lack of vacuum or something similar. I'll have a shufti around but don't know what I'll find.

 

[Myros]

all I could find was in the handbook

which says that aside from "brake" induced ABS malfunction, the system will switch off if the charging voltage drops below 10v, and will resume normal operation when voltage restored. A quick test with a voltmeter next time it happens will rule that one in or out. Barring any further input from fellow-sufferers, a trip to a mechie might be on the cards here. Best to be safe, as it is your brakes.

 

[timmo]

Thanks for the input Myros, I think the idea of checking the voltage next time it happens is a good one.
I don't think the uneven running is causing the problem as it is only just noticeable and only at idle.

 

[timmo]

I have now checked the voltage when ABS light is on and it is 13.8 volts.
Is the ABS linked at all to the idle control valve?

 

[Myros]

not as far as I know Timmo

except they have some vacuum input somewhere, although not common. I had fun with the idle control valve myself. It sounds like you might try some preventive/curative maintenance on it. Take it off, give it a good squirt inside with carb cleaner, or white spirit or Wd 40, then rinse out with a bit of petrol, catching the liquid. If you see lots of black particles and bits of gunk, do a proper clean, immersing it in white spirit or brake fluid in a jar for a couple of hours, then rinse and spit and try it on the car again. Good tip, if it has a part number, write it down before any of the above.
You can check the voltage across the plug on it as the car warms up, although you might need assistance in keeping the engine running while it warms up.
You can also test it off the car by applying voltage to the pins and seeing if the slide works (pen torch and squint inside).
From the symptoms you describe, it seems as though it is sticking in the "warm" position, and not the "cold" position. So it's giving you a lean mixture straight away, rather than leaning off with heat. If it is at fault.

Good luck

 

[timmo]

Myros, I took out the ovp? relay and it had been opened before.
I opened it and wedged the contacts over to their operating position with a piece of card and all is now fine!!

Do you think a new relay is required?

 

[Myros]

Dunno Timmo

although prudence would suggest yes., as it might just have been working properly, and protecting you from Over-voltage. If you've wedged it, then there is the remote chance, that you are over-volting, although your reading of 13.8 volts accross the battery during the trouble tells me you aren't. When I bought one for the C last year it was £47 inc. club discount.
Where did you find it btw?

 

[timmo]

location of relay

Myros, I found the relay just above the fuse bank in the drivers foot well!

 

[Myros]

I must go down there

and find my cruise control thing, as it does everything but cruise.
Good luck.

 

[classicsl]

cruise control ecu

mines knackered, apparently the ecu needs replacing. this, so i am told is located behind the dash basically somewhere above the driver side footwell and is a pain to get to in order to replace, and not only that, got a price from MB for the part.,...£467+VAT!! do we need to cruise....not at present thanks...got other things to sort. went in yesterday for an oil leak at front of engine, having some seals replaced but its feared that head gasket may need replacing....nice £500 bill on the way....