r129 low idle rattle

[Garista]

Hello,

Early 1991 300 SL r129, M103

I get a rattle sometimes just on starting when the engine is warm or it is a warm day.

It is when the idle speed seems very low, although it runs.
I know where the rattle comes from, it is not inside the engine but belongs to this external piston looking thing that attaches to the outside of the engine near the front. It is held by a nut and bolt, 13mm. I've tried loosening and tightening the bolt but it seems ok, it has a large washer on it, but the ring of the 'piston' thing shakes a bit when low idle because it has some play in it and this creates the noise.
Should this happen? Is it missing something? Also the extra low idle does worry me a bit. In the cold weather it is fine.

Otherwise the car starts and runs good.

 

[Jim2]

Hello,

Early 1991 300 SL r129, M103

I get a rattle sometimes just on starting when the engine is warm or it is a warm day.

It is when the idle speed seems very low, although it runs.
I know where the rattle comes from, it is not inside the engine but belongs to this external piston looking thing that attaches to the outside of the engine near the front. It is held by a nut and bolt, 13mm. I've tried loosening and tightening the bolt but it seems ok, it has a large washer on it, but the ring of the 'piston' thing shakes a bit when low idle because it has some play in it and this creates the noise.
Should this happen? Is it missing something? Also the extra low idle does worry me a bit. In the cold weather it is fine.

Otherwise the car starts and runs good.

A picture would help, if you can provide one? Engine oil is so much thicker when cold, and thinner when hot,so maybe that explains a part of your problem. Nonetheless, any kind of rattles / shakes etc are rarely part of the design.

 

[Garista]

A picture would help, if you can provide one? Engine oil is so much thicker when cold, and thinner when hot,so maybe that explains a part of your problem. Nonetheless, any kind of rattles / shakes etc are rarely part of the design.

Yeah usually it's so smooth.
I'm embarrassed but I think it may just have been a low battery...
I will do a pic of the part.

 

[Garista]

this is the bit that rattles anyway. side to side, or, front to back when facing the engine from front of car, when at very low idle.

 

[Jim2]

View attachment 76474
this is the bit that rattles anyway. side to side, or, front to back when facing the engine from front of car, when at very low idle.

That's a shock absorber top mount..the rubber bushings are worn and needs replacing. And most likely the one on the other side is worn too..ditto, the rear shocks. 4 in all. Looks very oily too..oil and rubber bushing do not mix. So I'd be advising you strongly to clean all the oil and crud from that area, and identify where the oil is coming from and fix it.

 

[Garista]

That's a shock absorber top mount..the rubber bushings are worn and needs replacing. And most likely the one on the other side is worn too..ditto, the rear shocks. 4 in all. Looks very oily too..oil and rubber bushing do not mix. So I'd be advising you strongly to clean all the oil and crud from that area, and identify where the oil is coming from and fix it.

Ah ok thanks a lot. I was wondering if there should be a rubber part. It was me who oiled it, other than the very old oily mess, I was trying to stop the noise, now I've cleaned it all, seem to be no oil leaks.
There are 4? I can only see this one... I will look. Thanks again.

 

[Garista]

There don't seem to be any other shocks like this on the engine. Just this one at the front. Are you sure?

 

[Garista]

It is just in front of the dipstick, below the engine bloc hoist ring.

 

[Garista]

Do you mean the suspension?

 

[rayhennig]

There are 4? I can only see this one

I noticed someone suggesting 4. The device you are pointing at is the belt tensioner damper. There's only 1.

I think they cost about 50€ from MB but about half that for a Stabilus replacement from AutoDoc. It may be worth replacing the tensioner when you're in there.

Good luck.

RayH

 

[mioba]

OP can you take another pic from a bit further out so whe know what you pointing it.

 

[Garista]

I noticed someone suggesting 4. The device you are pointing at is the belt tensioner damper. There's only 1.

I think they cost about 50€ from MB but about half that for a Stabilus replacement from AutoDoc. It may be worth replacing the tensioner when you're in there.

Good luck.

RayH

Yes, thanks, that seems to be it. I had a look at the Stabilus one, it doesn't seem to have anything the current one doesn't, but maybe I'll change it later. Got to fix wheel sensors for abs and the roll bar switch first. I'm going to ask about that in a new thread.

 

[Garista]

M103 inline 6 engine with CIS injection.

Ah the problem really is the too low idle at start up, and sometimes it takes a few turns to get it going. It was never like this, always started easy first time and so no rattles, and this happened suddenly. So - fuel or air?

I studied the CIS system on Youtube, and found it was (I think) the idle control valve (which controls the air bypassing the throttle at idle). I took it out and cleaned it, it was not stuck or clogged, but it was almost closed in its current position even when warm. So I tested it with my multimeter for resistance, and it has 0 ohms, no resistance, so is caput.

This valve is under the air cleaner box (you have to remove it) next to the throttle body. It has two tubes going to it, and it is in the form of a T shape with an electrical connector on the end.

Under there it was a bit dusty but no leaks off any kind and all is connected properly.

Well I hope this is the problem. I don't think it is anything more serious because the car, when it gets going, drives great and it idles ok when warm, if still a bit low. I'll let you know when I get the new part.

 

[rayhennig]

I had a look at the Stabilus one

I have both MB and Auto-Doc dampers. I think they are all Stabilus.

R

 

[Garista]

I have both MB and Auto-Doc dampers. I think they are all Stabilus.

R

Yes I saw the Stabilus one on Auto-doc, it looks fine, I probably will get one.

 

[Garista]

Well I put on a new (old) idle control valve but it has not really solved the problem with the too low idle at start up (it does still idle and start though, but it is shaky). I am suspecting either the cold start valve or simply the fuel filter needs changing. From the look of the old air filter I think I had better change the fuel filter anyway, so I can eliminate it from my enquiries.

 

[Garista]

Ok, I changed the fuel filter with a Meyle original one. I also cleaned the little pre-filter which enters the fuel distribution block. This had some stuff in it. Then for a while it seemed better but then got the same thing back, very low idle, and then it got even worse and stalled on start up, then would not start without a lot of pedal. I looked at the plate in the fuel distributor and it was fully closed on low idle, which did not seem right. Anyway, in the meantime I had put on two new speed sensors, which had not been working. I decided, after inspecting it all again, to put back on the old and cleaned idle control valve, and restarted the car and it started and ran fine again! Test drive again it started and ran fine. Problem gone away!

So I think it was a fuel filter problem.

The dash light for the abs, in all this process, had gone off, but it came on again, ha! But car drives even better now, I notice the gear changes much more, fast and deliberate, and the engine seems quieter and smoother, more power. I think the abs is working but the dash light is staying on and maybe I have to clear the codes but I don't have a bleeper thing (OBD 1). Is there a way to clear them without a special tool?

 

[Garista]

Oh yes, by the way, for the hydraulic tensioner damper, I replaced its soft washers which solved the vibration, otherwise it was still ok. Had to take off the fan, and the water pump pulley to get to the lower bolt, but it was all quite easy. Was a good time to clean it all down there.

 

[rayhennig]

I changed the fuel filter with a Meyle original one.

What does "Meyle original" mean?

Meyle is a supplier of parts of variable quality, best avoided if you are serious about your car. Mahle, Mann or MB would be my choice for filters.

Good luck anyway.

R

 

[Garista]

What does "Meyle original" mean?

Meyle is a supplier of parts of variable quality, best avoided if you are serious about your car. Mahle, Mann or MB would be my choice for filters.

Good luck anyway.

R

On the advert it said Meyle 'original equipment' or something, from Autodoc.fr. Oh well...