Sorry, I hate acronyms myself but the two below are common around here.

NA : North America
HVAC: Heating-Ventilation-Air Conditioning (AKA - Klima in Europe)

Yes Fuel injectors leaking air is particularly bad because that is unmetered air not coming thru the AFM plate.
The plastic inserts and the rubber seals should be replaced periodically (I would say every 20 years for daily usage). It is an easy DIY job as long as you do not strip the aluminum threads by overtightening the bolts that secure them to the intake.

If your mechanic noticed they are leaking air and did not insist on changing the seals I would question his judgement.

However he could have meant the injectors are going bad because they are not holding fuel pressure by dripping after the car is turned off. That is more likely because that would be noticeable. You will see wet spark plugs and the fuel pressure dropping rapidly after the car is turned off. Air leaking will require a smoke test or a propane test.

- Cheers!

- Cheers!

Oh I see, I kept thinking of the HV as high voltage I could not figure out what it had to do with the car.

No no, he did change them, this is part of the work he did about 10 years ago, after which the car has been running like new until recently.
This is something I can ask to check next time I go.

I guess the fuel pressure is something that you don't measure without some special tool, right?

If he has changed the injectors and seals 10 years ago you are set. My originals lasted 26 years at which point the injectors were replaced along with the seals.
If you have relatively new injectors you are probably ok there too but for this purpose you can use any fuel gauge with the correct couplings.
If you do not have one I would just purchase one made for the MB jetronic. Then you can also do FD tests in the future. They were about $110 when I purchased mine.

But honestly, I am not hearing anything here that would cause a lower than acceptable vacuum in your intake. If you still suspect vacuum loss in your injector seals you should just check for that.
Some people do a propane test which is a but dangerous.

There is a Y splitter near the firewall on the intake side. One output goes to your gauge the other does other things. Plug the one going to the "other things" an see if the vacuum changes.
Or better yet plug a vacuum meter (with a scale) on the "other things" port an make sure your gauge is reading properly. Full scale on your instrument cluster is 17 inch-mercury.

Hi, sorry, it took me a while to get a few measurements.
I've got a vacuum pump with the gauge, although I would not bet anything on the accuracy of the 18€ tool, so I would take the reading as "indicative".
I have checked the vacuum lines going to the lights and they are fine, they hold vacuum.
I have checked also the vacuum line at the splitter near the firewall and the lines going past the firewall are also holding vacuum fine.
When I tried the line going to the economy gauge I could get it all to the left, although the pump gauge was reading about 19 InHg... but again, I would not know how calibrated it is.

On the other side, on any other pipe I tested, I couldn't get vacuum. I suspect the pump doesn't hold the vacuum so I can't test the lines connected to it, but this is just my guessing, I don't know if it's correct or not.
What I have noticed is that there is strong smell of fuel when I pump from those lines (for example the one going to the ignition module (the module number 008 545 92 32, sorry I'm seeing so many acronyms that now I don't know which one is the right one for this part). Again, I don't know if it's expected or it is indication of a fuel leak from the injectors, no clue. I actually have forgotten to mention that I could smell clearly fuel also when I was moving the air intake plate while I was taking the measurements.

I have taken a short video of the pressure on the vacuum line, maybe you see if it is normal this behaviour on idle-acceleration-idle.
If the reading is correct, since it's holding around 17 InHg in idle, then it would look like the gauge is not reading correctly any more, but still the engine doesn't seem to run properly to me.



https://youtube.com/shorts/Db9x11Lw_8Q

Thank you in advance for any feedback!

I would trust your new vacuum gauge more than a 30 year old one to be honest. It that is saying you are reading about 17 inch-mercury, you are OK. Your cluster maybe be getting a little oldand tired.
I would worry about other running issues if you have any other issues.

- Cheers!

So I have done a few more tests today.
The air plate potentiometer works fine, and I have checked also the idle control valve and it makes a beautiful free-moving sound when connected to power. The voltage on the connector is also the battery voltage, so it's good.
I have been pushing down the electrical connectors on the ignition module that, for some reasons, were half-way out, but no change (which is, let's say, good).
One of the vacuum pipes beneath the air filter box has been "sanded" by years of vibrations against the bottom of the air filter box and it's flat. It will eventually break, but I tested it and it's still good.
So far, everything I have tested looks good.

So, trying to explain why I'm bothering with these checks... let's admit that the economy gauge has now an offset and in idle is not going to full left any more. Even so, when I plug the AC, the RPM remain fairly stable but the economy gauge goes to middle of the scale. This was happening also many years ago before the mechanic fixed (or adjusted) everything, and afterwards you could not even feel the engaging of the AC. Also, when the AC engages, you feel a significant loss of power, which was also happening before, and now it's back. [edit: here I mean loss of power also while the car is running, not just in idle]
Up to here, the objective observations.
Going into the realm of feelings, it feels like the car is consuming significantly more (I still have to drive enough to take a measurement, but the fuel gauge has gone from full to less than 7/8 in 70km of motorway, and I used to do 11-12km/l, measured over a number of years). Also, it does feel less responsive.

What is left to check that I can think of are spark plugs (which never made any real difference, as far as I could tell) and injectors. Car has been serviced 8 months ago but I don't think they changed the spark plugs, I need to check in the invoice. I know for sure that injectors were involved in the previous work that magically brought the car back to its youthfulness.
I have seen where the injectors are, but I don't feel too enthusiastic about working on the fuel lines, so I might take the car to some garage and ask them to check both plugs and injectors and eventually replace them.

It is perfectly normal for the vacuum gauge to go down a little with the AC on. There is more load on the engine and at the same RPM the IACV opens a little more to let more intake air in.
All W201's/W124's do this.

Your spark plugs look perfectly fine to me but that is only a 12 dollar investment if you choose to make it. Does not hurt the put in new plugs.

Injectors are not consumable items, my first set went 175K miles. The dealer insisted I change them and it would improve my California Smog test numbers.
At the dealership it was done at the considerable cost. They did not improve my smog numbers, actually made them worse. They refunded all the cost in it's entirety.
True story. Not all injectors would go that long but as long as you use gasoline with techron or other additives (shell stations also have this in the US, I by Chevron exclusively).
Does my car run a little better with the new injectors? Of course, but the dealer told me is if I used gas with techron additive it will never need another set of injectors.

Not sure what else could be an issue with your car. I would also do a compression test at some point. Or better yet a leak down test. I found out one of my cylinders is actually worse then all the other 5 thru a leak down test. It was acceptable but certainly noticeably worse.

Indeed, as you say, a little. Now it's going down half of the range, which has not been happening in the past ten years or so.
Also, sometimes I disable the AC when I have to leave at a roundabout because the loss of power is so noticeable that the car lacks of acceleration.
And what seems to be a 30% increase in consumption is also there (even without the AC running).

Actually, I was just thinking about the petrol. In UK almost all petrol now has gone to E10, I found a note from Mercedes back then saying that these engines should not run on E10. For some time I moved to the unleaded 98, which was still E5, but it quickly became not affordable any more. I wonder if the use of E10 fuel might had something to do with that. Here in Spain it looks like the unleaded 95 is still E5.
I'll check the addictive that I can get over here.

Ok I'll take note, thanks.
One thing about leaks. While reading about how to change injectors, they were mentioning to remove the fuel pump relay, crack the engine three times to empty the fuel lines and remove the pressure and then start the work.
So I understand that, if I have leaking injectors (and from what I read, within the symptoms there would be increased consumption -I have it-, long cranking time -I have it- and smell of fuel -I get a lot when I open the air intake plate-), the pressure on the fuel lines would go down quickly once the pump is off.
As a quick, dirty check to see if it's my case without removing too many parts, could it be an idea to run the fuel pump two or three times, wait let's say five minutes, then loose one of the fuel lines from the distributor to see if it's still pressurized?

If you intend to keep your car for a long time I would instead buy a fuel pressure gauge and connect it to the testing port on the Fuel Distributor. It will tell you if there is a leak and how bad it is.
I suspect a leak in my engine for years. Turned out I do not even have a leak. This also is very non disruptive, and you are not potentially damaging injector seals etc. If you go your way, I woul purchase the injector seal kit first as most likely you will replace them.

If you do have a leak, there are many sources for that and your relatively new injectors are probably at the bottom of your list. Unless they were defective.

But you are very good with instruments, you should get a gauge. They are cheap, an in europe you should have trouble finding the metric brass couplings for the pressure gauge.
A bit harder here, though one meant for mercedes comes with the coupling.

Well I do hope to keep the car for a long time, it was my father car since the 1990 and I have spent the last 33 years on it, first in the back seat and then in the driver seat. Apart for the very first months, it has always been in my family.
Ok I'll look for the fuel pressure gauge.
Thanks again for all the suggestions, your help has been precious.

Very good to hear. Hopefully my son will take over my car some day. He is into cars and manual transmissions, particularly. I am the original owner of my car.
My son is helping me rebuild the clutch and the transmission at the moment.
If you want a good pressure gauge meant for these cars and you can find this in Europe, I would highly recommend this one in the picture.

- Cheers!

Thanks, I was actually looking for that one because it was recommended in a video I have seen, but it looks impossible to find it on this side of the ocean.
Anyway, today I have noticed another thing that seems not to be working as it should and could actually be the cause of these issues: the alternator seems to be unable to provide enough current.
When I switch all lights on, including foglights, for some time the light indicating a burned lightbulb was coming on intermittently. I blamed the fuses that were not making proper contact (they were still the original and badly oxydized, I changed a few but they run out, so I could not replace all of them) because when I checked the voltages in the fuse box they were a bit low.
Today I have noticed it again when I took the car for the inspection (luckily they didn't ) and when I arrived at home I made a couple of checks. With no lights the voltage on the battery is 13.3V, which goes down to 12.6V with the lights on and keeps dropping (I have arrived to 12.4V after a few moments). When the voltage goes down, the light warning goes on, although no light is actually off.
Increasing RPM seems to increase the voltage only marginally. The battery is new (changed it 6 months ago).
The alternator board had been changed about 20 years ago, I think, because it was not charging properly any more. The alternator itself, I think it's still the original one, although the bearings had been changed 13 years ago because the main bearing gripped.

So time to start study the electrical diagrams... here is where I feel more in my comfort zone

That is a problem. In my car with all electricals operating it never goes below 13 volts. I have installed a voltmeter in the car to monitor this 24/7.
You may start with replacing the voltage regulator which is easy and is a small investment in time and money. If that does not work you maybe looking for a remanufactured alternator.

With no load an a fully charged battery the running voltage is ~13.5Volts. When I turn on all accessories it will drop as low as 13Volts.

It took me a while to get hold of the new alternator regulator (first time Amazon failed a delivery...), but I finally got it yesterday and mounted it in two minutes. Now the voltage is 14V steady, going down to 13.7V with all lights on, so quite an improvement.
I'll keep you informed if I manage to get something else sorted out.
By the way, I would like to change also the blower motor because the bearings are doing that annyoing gneek-gneeek-gneeek sound the whole time, but I'm struggling to find the correct part number to find a replacement. Do you have any suggestion on where I could look, to be sure that I'm getting the right one?

I have not had to change the blower motor on my car. I read it is a lot of pain and you have to put in an aftermarket motor as OE manufacturer (Bosch?) no longer makes them.
I would first try to oil it if you can. Sorry I'm no help in this one.

Great to hear your new regulator solved the low voltage problem.

Happy Motoring!