W124 M103 idle shake. Age vs Mileage

[ndevlin87]

I daily drive a 1987 300ce with just over 40k miles. Since I bought it a year ago, it's had a slight shake at idle when in drive or reverse. The revs do not fluctuate, but every second or two you get a slight shake from the engine that's felt through the body. The car also jolts when shifting from drive to reverse. It idles pretty much perfectly in Park or Neutral, and drives surperbly.

To try and improve things with the shake (and also just as preventative maintenance) the following parts have been replaced with new items:

Plugs
Plug wires
Fuel Injectors and seals
Over voltage protection relay
Idle control valve
Distributor cap
Rotor arm
Fuel filter

One of the problems I have with trying to diagnose the issue is the mileage of the car. With only 40k miles and having been garaged for the vast majority of its life, everything in the engine bay looks very fresh, with parts such as vacuum lines and bushes showing no evidence of cracking etc. However, given its age and how rarely the car was used, many parts seem to have dried out and hardened up despite looking as good as new on the surface. A case in point was the anti roll bar bushes. Looked perfect, but replacing them and the associated brackets totally silenced the squeaky suspension on cold mornings.

As such, I was wondering what you all thought about my prospects with changing the engine and transmission mounts in terms of reducing vibrations?

Again these are rubber parts filled with fluid that on the surface look perfect and everything I've read suggests they shouldn't need to be replaced until well over 100k miles.

Basically should I be ignoring all the mileage guidance on the longevity of parts, due to the fact that the car is now 28 years old?

 

[Ian B Walker]

check engine mounts, gearbox mounts and while you are there check the prop shaft doughnuts.

 

[grober]

Sounds like an intermittent misfire under load. This can be down to a lean mixture or weak spark. At 1987 your car may not have a lambda sensor to compensate for a weak mixture.
This could be down to some form of inlet manifold associated leak- lots of flexible pipes vacuum take-offs to leak.
In terms of ignition did you use pukka MB parts for the HT. Cheap pattern parts often break down in a short time.
I would take a look at the plugs to check for weak mixture and maybe get the car on an exhaust gas analyser to check mixture strength.
A study of the plug firing lines on an old oscilloscope type engine analyser would show up any HT breakdown. Some garages still have em in back somewhere.

 

[ndevlin87]

Thanks guys, good information on both the engine and bushes side of things.
Everything has been replaced with proper mercedes parts, apart from the HT leads, which my garage replaced at short notice due to a bad misfire shortly after taking the car home. I'll replace these with mercedes parts whilst checking the plugs (proper Bosch non resistor type) and see if there's any difference. Also, my car has no catalytic converter, did these models ever come with an lambda sensor, despite the lack of cat?

 

[grober]

Thanks guys, good information on both the engine and bushes side of things.
Everything has been replaced with proper mercedes parts, apart from the HT leads, which my garage replaced at short notice due to a bad misfire shortly after taking the car home. I'll replace these with mercedes parts whilst checking the plugs (proper Bosch non resistor type) and see if there's any difference. Also, my car has no catalytic converter, did these models ever come with an lambda sensor, despite the lack of cat?

Don't think the non catalyst cars came with a lambda but would not swear to it-- is the car jetronic K or KE Injection? I would still get the mixture strength tested on an exhaust gas analyser - as used by all garages for MOT testing. MB plug lead set with the built in suppressor/resistor at the end that clips on to the plug are expensive.

 

[John Jones Jr]

it's had a slight shake at idle when in drive or reverse. The revs do not fluctuate, but every second or two you get a slight shake from the engine that's felt through the body. The car also jolts when shifting from drive to reverse.

You may have two issues rather than one. Gearbox and Engine.

First up, I'd carry out a gearbox service - fresh oil & filter along with a gasket. Second, I get someone i.e. a Merc specialist to check the gearbox and engine operation. Sounds like a nice car so I reckon it's worth getting things right.

As for perished/failing rubber components, I suspect time rather than mileage will have taken it's toll. But where do you stop, as there's plenty of rubber components? But I would replace the engine & gearbox mounts regardless and go from there. Maybe the front shock top mounts too? Also check the date stamp on the tyres!

 

[John Jones Jr]

Forgot to mention. If you haven't done so already give the car a good motorway blast, even find an excuse to to take a long trip with using plenty of rev's. Throw some fuel cleaner into the tank too.

 

[ndevlin87]

It's had a full gearbox service early last year. And it's a KE jetronic fuel injection system as far as I'm aware. Oh and I fitted a new set of Continentals, the previous tyres were over 10 years old. Makes sense when it had driven less than 1000 miles in the last decade.

So, engine and gearbox mounts, HT lead set, and an exhaust gas analysis/ spark plug check to investigate potential for spark/mixture issues. That and a vacuum leak investigation.

As far as a good blast goes, went on a 150 mile round trip to Loch Lomond and back yesterday, and since that the shake has gotten worse, which it hadn't done for months.

It's a nice car, looks a fraction of its age, would love to get this sorted as its a fantastic thing apart from this relatively small issue

 

[John Jones Jr]

As far as a good blast goes, went on a 150 mile round trip to Loch Lomond and back yesterday, and since that the shake has gotten worse, which it hadn't done for months.

If you don't mind me saying so, hopefully the shake now continues to get worse, as then in theory it should be easier to diagnose what's causing it. Don't throw any more parts at the car would be my advice bar a set of plug leads as that's worthwhile preventive maintenance.

 

[John Jones Jr]

Have search online for OVP (over voltage protection) relay, these do go faulty and can cause several issues.

 

[ndevlin87]

I followed some advice on Mercedessource (a great site if you haven't heard about it) about checking for worn engine mounts. Open the bonnet so you can see the engine through the gap, put the car in Drive, put one foot on the brake and gently press the accelerator, looking at how much the engine lifts at one side, then repeat with the car in Reverse. Looks like one of my engine mounts has collapsed, as the engine lifts up at least an inch at one side. The other mount doesn't seem to be as bad.

It also might explain the jolt I've been experiencing when shifting into reverse, as it's the mount that experiences more force in reverse that is the most worn.

So definitely time to replace the engine and gearbox mounts I think, in addition to the fuel/spark checks that you guys have suggested.