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82' 280E, 86' 190E
2 Posts
Discussion Starter #1
Hi All

I have an '82 model 280e that I've owned for about 10yrs.
This car has done about 450000 Km (miles???), and I suspect the motor may have just about had it. For the last 6-12 months the idling has been getting rougher and rougher, tends to feel like its only running on 3 cylinders ! Once it gets over about 1200 rpm, it smooths out and runs normal with plenty of power.
The problem is, where to even start with diagnosing the cause of the rough idling, and with a car that has travelled this distance, would getting the motor reconditioned be the only option ? I ask because it still never uses any oil, oil pressure gauge still reads high and power is good when it gets going.
I've tried a few obvious fixes such as changing the plugs and oil, air and fuel filters. One MB mechanic thought it could have a burnt out valve, but don't these cars have hardened valves ?
BTW, where I live (rural Australia) it seems to be very hard to find a decent MB mechanic that I can trust ! so any advice anyone could provide me with would be much appreciated, just so I'm armed with a little more info next time I front up to the local mechanic [:)]


2017 Police Interceptor Utility, 2017 Police Interceptor Sedan
7,747 Posts

I believe, rough idle alone is no reason for an engine rebuild. It's entirely possible that you have one or more stuck or dirty injectors, spark plug wires or any number of other things. When was the last tuneup? When was the last injection cleaning? I would certainly attempt those before condemning the engine especially given good oil pressure and consumption.

On the other hand, at 450000km (about 280000 miles) it's not like that motor owes you anything. If the vehicle is otherwise in good condition and you'd like to keep it, a rebuilt motor might be advisable if you can find one at a reasonable price. Here in the US, they can be had for about $3500-4000 remanufactured to factory specs. I don't know about Australia.

Hope this helps.


1989 W201.029/M103 3.0
244 Posts
The rough idle may just be a valve adjustment. M110 motors, as far as I know (my brother in law has one, not me...though I'm saving for a Benz now, my expertise is other engines), use a direct valve lifting mechanism which requires periodic adjustment to maintain tuning.
I had the same problem with a wild cam grind I had fitted to a street/strip car I was running with adjustable rocker gear. Great for cam following but you sometimes had to pull over and adjust it in the middle of a cruise for top notch performance (spinning the wheels at 80 and silly stuff like that).

This would seem like a burned out valve to a mechanical diagnosis by someone who isn't used to such an engine.

That being said, at 450,000km I feel arbitrarily certain you need all new bearings, pistons, rod guaging, bores and valve gear as part of a general reconditioning on any engine from a Ferrari 308/GTS to a Holden 48/215.

If you want to do it on a budget, contact a Mercedes wreckers (pm me and I can give you the location of a good one in Melbourne from my bro-in-law), and get a low km second hand M110 in good running order (say, 150,000km), shipped over to you at the standard transportation cost.
Maybe Mercmad could also help in this department, he's far better at this than me.

Otherwise, get out your toolkit, set up some space in your garage and pull the thing out of the engine bay and send the head off and block off for a full reconditioning.
Get the head flow benched for a few cc's more of intake/exhaust rates if you can afford it too, whilst you're at it, the M110's could really use a little help in that department. And make sure it's got new, Euro double valve springs fitted.

Make sure you get the Euro high-top pistons as well (9.2:1 static compression). And a full bottom end balancing to fine tolerances. Tell them you're thinking about racing it (lie).
Many Aust. imports had flat tops and single valve springs as per the US standard grade unleaded/emissions variant from 1977 (but not all, Euro's still snuck through as my bro-in-law has a full Euro spec 280E 1981 import...goes okay for its engine capacity and vehicle weight too, I'm impressed enough to be saving for an M114 presently).
The California engine would be a seriously whimpy variant by comparison and Australia's emissions laws are far more slack (we have so much more space and far fewer cars on the road over here).
So if you've got the flat-tops, toss 'em.

Also select a custom cam grind as part of the rebuild, some mild aftermarket job that makes best use of the overlap and centrelines for a bit of extra grunt at a relatively stock idle and emissions output. If they don't have anything off the shelf just see if you can get a few more degrees of duration and a little more valve lift with a basic regrind. Say something like, "I want about 8-10 degrees more duration (edit: at 50-thou) and 10-thou more lift on the stock profiles," and that should do the stock driveline setup perfectly.

With all that together that should get outputs a bit more worthy of a modern Merc badge (around 210hp), and a nice, reliable engine that should last you at least another 450,000km.

Dunno about the transmission/unis/diff and driveline balancing though. Get some work done on your brakes and steering too. And definitely replace your entire suspension.
Hey, you're the one with all the kays.
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