Mercedes 230TE (W124) stalls when slowing down/ braking (at traffic lights and on slow corners etc).

Last Updated on February 18, 2023

A couple of weeks ago I picked up a 1991 Mercedes 230TE (W124) estate car for just over £500, it was a cheap price and as the current owner had put a year’s MOT and tax on it I considered this car purchase a tolerable risk. The tax alone is worth nearly £200.

I chose the Mercedes W124 because of its legendary reliability; it is the last of the truly over engineered ‘built to last’ Mercedes. The W124 hails from an age before Mercedes started competing with the influx of cheap Japanese cars that were flooding the market. In fact legend has it that the engine of the W124 Mercedes was designed to last for one million miles! This puts the fact that the example I have bought has done 170,000 miles into some perspective. 170,000 is also fairly low mileage for a 230TE that is nearly twenty years old.

The Mercedes W124 are also incredibly comfortable and most examples have an automatic gearbox. I haven’t owned a car for over a year and this beast of a motor serves as the perfect antidote to the tiny Daihatsu Hi-jet my wife owns (and sometimes lets me drive).

Part of the reason the car was as reasonably priced is that there is an intermittent fault, although since I picked the car up the fault has been less intermittent and more permanent.

The problem
The car stalls when slowing to a halt, in much the same way as a manual car would if you forgot to put the clutch down just before coming to a complete standstill. My Mercedes will also stall when slowing hard on the brakes, essential when going round a slow urban corner.

I’ve never owned an automatic transmission car before, in fact I’ve only ever driven an auto twice in my life, both times in America (and on the ‘wrong’ side of the road). When the engine first stalled out it took me swiftly to panic stations. The fact the handbrake is operated by a foot pedal and released by a pull handle on the dashboard only confused the situation.

Now the car stalls every time I have to hold down the brakes when going less than ten miles an hour, its damned inconvenient but I’m a fairly calm sort of chap and (so far) other road users have been quite tolerant of my unscheduled stops. But this MUST be fixed, in this state the car is quite simply unusable and is verging on being unfit for the roads.

Restarting the engine is never a problem, but when it’s stalled three or four times in a few hundred yards the smell of petrol can get a bit rich. I’m also sure the engine starts to flood a little, which really won’t help the problem.

Mitigating…
The previous owner of my car was a Mercedes fanatic; he had personal plates on this car and kept it maintained above and beyond the call of duty. This was probably partly due to the fact the previous owner makes a living selling Mercedes W124 parts online. My 230TE was not bought from some wide-boy who had thrashed the car to within an inch of its life.

In trying to solve the problem the previous owner replaced (with genuine Mercedes parts) the alternator, the HT leads and a whole bunch of other stuff, but all to no avail. As the fault is intermittent he was unable to get the car to a mechanic while the fault was occurring. In his own defence he admitted quite candidly that he sells Mercedes parts, he is not a Mercedes mechanic.

The solution
Well I haven’t found a solution just yet, and I will keep posting updates on this page until I do.

I called out the friendly mobile mechanic (Kevin) who keeps my wife’s Daihatsu Hi-jet on the road and bar tightening a loose hose (he found under the air filter) he was unable to offer much help. It’s not to say he didn’t try; he pointed out that a small hole in the exhaust was probably affecting the amount of CO2 in the engine, and until I got that hole fixed it might prove something of an obstacle to diagnosis. He recommend a local independent Mercedes specialist and I duly booked the car in for repair of said hole. As I sit writing this up that appointment hasn’t happened yet (it’s Friday and it’s booked in for this coming Monday).

Having owned several old and character full cars in the past I learned long ago just own valuable Internet forums are in solving problems. Forums bring together hundreds (if not thousands) of people all interested in the same car as you. Wherever there are these thousands of enthusiasts there will always be plenty of people that have found themselves facing the same difficulties that you are trying to solve.

Some helpful people over on the W124 section of the MBworld.org site feel sure that this stalling/ engine cutting problem is due to a problem with the OVP (over voltage protector). This small device that can be found lurking behind the battery stops electrical surges from blowing out parts of the car’s systems that would be expensive to replace. The fuse on top of the OVP was fine, but the users of the forum inform me that over time water leaks into the OVP unit somewhat diminishing its effectiveness.
The previous owner had his suspicions that the stalling at low speed was being caused by a vacuum leak, but this idea was soundly poo pooed by our friendly Merc geeks on the MBworld.org forum; they pointed out I’d be having all kinds of other horrid problems, which I’m not.

Here’s the thread over on that forum…

A quick chat with the parts people at my local Mercedes dealership (preceded by lots of long confused phone calls with local scrap merchants/ breakers yards) revealed that a brand new OVP unit could be mine for just £70. At this price I decided to take the risk of replacing what might be an already working part and jumped in my car and headed across town to hand over some cash to said franchise holder. Pausing only to stall ten or eleven times of course. So now I’m the (proud?) owner of a brand new Mercedes OVP unit, and tomorrow morning I’m going to fit it and see what happens, I’ll report back here of course.

Update – 14/11/09
The new OVP relay was very easy to fit, in fact I don’t think I’ve ever done any work on a car that was so brief and easy. I took the car for a spin to see if it would still stall. I held the brakes on corners, held the brakes at traffic lights and generally did everything I could to make it stall and it didn’t. I was feeling cautiously optimistic, and decided to go to our local farm shop to buy some gourmet mayonnaise (I tell you this, because sometimes details are important) and had to hold the brakes for an age waiting to turn into the entrance. Shudder, poot, the engine stalled.

I gave up on buying Mayo and headed home. My optimistic side is trying to tell me that the stalling problem wasn’t as bad, but my pessimistic side is telling me that if the Mercedes specialists can’t fix this problem on Monday then I may have to sell the car. I’ve only had it two weeks and have only done 115 miles, and 100 of those were the drive from where I bought it to my home!

Update – 16/11/09
I’m just back from the independent Mercedes specialist ‘Prestige’ in Ipswich with some good news, some bad news and some weird news.

The good news.
The idle circuit air hose was badly split so they taped it up and ordered me a new one, cost is just £12! This will probably almost entirely eradicate the stalling problem. They noted on the diagnosis report that the OVP unit had been replaced, so I feel kinda like I did the right thing in replacing it.

The bad news.
The exhaust manifold is cracked and the oxygen sensor has become one with the rust therein. The catalytic converter is also shagged (my word, not theirs). So there’s air rushing in where air ought not to be rushing in, and the engine is getting all confused and running far too rich (hence the petrol smell I described earlier). The catalytic converter is contributing to the problem by kinda suffocating the engine, thereby twisting the knife that cases the stall. A replacement oxygen sensor will cost about £136.00 (not too bad), a new catalytic converter will cost £1162.00 (oh mercy).

The weird news.
The idle circuit air hose will be fixed within the week, and should almost entirely eradicate the stalling problem, in fact it’s already FAR improved with the Heath Robinson repair they put in place today.

If I’m happy with the performance of the car after the hose has been replaced then fine. If it’s still an issue then they’ll replace the oxygen sensor, mig weld up the holes in the manifold and remove the catalytic converter entirely – it turns out cars as old as mine don’t legally need one! So I’ll feel a little bad that my car is chucking out some nasties into the atmosphere, but that will be nicely balanced by the fact that I’m keeping an old car on the road! Keeping an old car going (to a certain extent) is surely better than buying a brand new car? Replacing the catalytic convertor is quite simply never going to happen, in fact if I was forced by law to replace it I would have to scrap the car as I can’t afford it!

Update 29/11/09
When I took the car in to have the new idle circuit air hose fixed the garage informed me that they’d found a non-Merc catalytic converter for £120. The car does drive better with the new hose but once I’ve started stalling I know the rest of my journey may take ‘some time’.

So I’m going to clear out the remainder of my non-existent W124 budget and buy a new cat £120 (US$200), a new O2 sensor (about the same price) and then pay the garage a few hours labour (at a very reasonable £60 an hour) to fit the parts and weld shut the hole in the manifold.

So fingers crossed this will fix the problem, because if it doesn’t I’m going to be driving this car until the MOT runs out in November then I’ll have to scrap it!

Update 04/12/09
I saved up £500 to get the o2 sensor and the catalytic converter fixed. The split in the manifold also needed sealing up and the garage was also going to attend to that.

I woke up extra early to get the car down the garage, ‘this is the day’ I thought. I cheerfully mused to myself that when all the work was done by the end of today I would have a lovely car that I would keep for years.

With a song in my heart I turned the key in the ignition; well at least I tried to. The key wouldn’t budge and in my attempts to turn it I managed to lock the steering. No amount of gentle jiggling would free the ignition or the steering column so the garage sent out a professional key jiggler but he agreed things were looking grim.

So in addition to the o2 sensor, the catalytic converter and the welding on the manifold I was now in need of a new ignition system, steering lock and steering column parts. Even if I used pattern parts this would add about £350 to the current expected bill of up to £500, this brings me to a total of £850, which if you’ve been following this sorry tale is more than I paid for the car in the first place. So the end has come, the garage are going to recover my car to their premises and rape it off anything valuable in lieu of their bill for today’s work.

So I owned my 230te for thirty days and drove it about eight times. My wallet hurts so bad I can’t sit down without wincing. I haven’t owned a car for a year and a half and then once I had saved up the cash to buy one I just pissed £800 (US$1400) down a big black hole.

I’m done, I can’t afford another car, and considering I’m an IT consultant that has to go on call out this is not what I would call a happy ending.