Gyri

My 1996 Petrol E220 W124 (HFM type) engine (111.960) every now and then annoys me while accelerating. This happens once in maybe 3 KM of running, with or without the aircon ON. When it happens, it basically for a second doesn't respond to the accelerator input and then lunges forward jerking-ly. I have found that when it happens, I can get over it by depressing the clutch pedal and then pumping the gas pedal fully a couple of times. It then resumes to running normally, until maybe a few KM later. This can happen during gear shifts or while giving throttle inputs from steady speeds.
OK, the story before this is that the car used to stall much like W124 s described in many other threads. I had MB authorised men have a look at it with their diagnostic tools, all in all they had my car for a month and a half.
First it was the Engine wiring harness which was re-insulated by them for almost 1/3rd the cost of a new part. Then all filters (air, fuel, oil) were replaced. Fuel tank cleaned, New throttle cable, new spark plugs, new fuel pump (the old one was whining, but load and delivery test showed it performing well). OVP relay was visually checked and it was the new SIEMENS one, so that was ok. Throttle body was cleaned. The diagnostic kit showed all the sensors to be working fine. Well, the engine doesn't stall anymore and I haven't noticed any abnormal RPM hunting off late, but then every now and then she behaves as though she moves on square boots
Ran the tank through a can of injector cleaners, No luck!
Naturally, MB gave me a list of components to change, which pretty much excluded only the body panels. It was time for me to take my car and leave.
So here I am.
Any and every bit of help would be very much appreciated!
Thanks in advance!!!!
BTW, my car has run 41000 KM.

RunInColorado

Im not sure if this helps or not but I thought I would add my experience (well experience with mothers car). She drives alot around town with low revs and often the car will do the same thing you described. It has had fuel tanks, filters, etc changed and checked. What I have found that seems to cure the problem is to keep the car in the higher rev limits 4000-5000 for a while. The car settles down and works just fine for a couple months. I woudl say this is because of the carbon build up but I could be wrong. Good luck!

Gyri

Thanks for the reply, my first in this forum.
A few weeks back I did try driving the car with higher revs, basically shifting much later, it helped very little. Regarding carbon build up, I have cleaned my engine with a good quality "engine flush" prior to the last oil and filter change. Didn't really make a difference in the performance. One thing I did notice while driving with high revs, is that the engine cuts off at 4000 RPM, much like it does when in IDLE. I need to take it back to the service guys to check it.

Bubb Rubb

It sounds as if you are intermittently losing either spark or fuel (maybe both?). You can start with checking the easy stuff, such as checking (or cleaning!) all the electrical ground connections.

I sympathize with you, as intermittent problems are hard to diagnose, since the symptoms are often only there intermittently!

You deserve a round of applause for your description of the symptoms and the conditions under which the car acts up. Many people seeking help fail to explain the whole story and don't detail all the various conditions under which a problem may occur, as you did. Good on ya!

Gyri

Thanks Bubb. It's like a kid hiding all it's illness at the doc's place to avoid the shots. I have had a lot of practice at the MB service centre, where the car would just be perfect.
This one time (maybe a year back) I drove with a MB engineer for an hour in heavy traffic and then on a highway for another hour and all in all the car just mis-behaved once. And the Engineer kept looking dead straight as though we just ran over a rumble strip and nothing wrong happened. It was good that I insisted on reading the fault register from the memory when we got back to the garage. At that time it read " Possible false air". They just cleared the memory and had me on my way home.

I'll definitely run through all the electrical grounding in the car. I am also going to recheck all the sensor harness(s).

Gyri

Just thought I'll keep everyone updated. I managed to locate a friendly dealer, who after a lot of convincing has agreed to lend me a new throttle body to try out in my car. I did try to milk him for an air-mass sensor too, but then he didn't have one in stock. Guess he was worried, if I'll ask him to lend his house too. If everything goes well, I'll do the swap in a week's time or less.
I read in a few posts that throttle bodies tend to fail quite commonly when there are issues with wiring harness, which I did have. Check out http://www.bba-reman.com/throttle_body.htm .
While I do suspect a lot of other commonly failing components such as O2 sensors, CAT choking, Air MAss sensor, Purge valve, spark plug resistors and coils, the symptom isn't an engine cutting out or a misfire as in an electrical disconnection, the car idles well, although it sometimes jerks heavily on small throttle openings. So maybe, just maybe it isn't an electrical/ignition related issue/component.
With regards to improper Airmass Sensor ( which normally shows up as "check engine Light" and not so far in my case), O2 sensor, purge valve or bad injectors, I should be having some cold starting problems (none so far, fires up immediately) and sluggishness during acceleration (not so, she accelerates well). This week, I'll get my fuel consumption figures when I tank up and also run a "Pollution Control" test (that's what we call it here in India). These two will further give me something to chew on.

mjtray

Gyri,

It does sound like the start of an Air Mass Sensor problem....they are very sensitive to contamination. If you have a dirty air-filter, dust can contaminate the hot wire in the MAF.

In theory it should burn off, but if it does'nt it can create flat spots, poor running, heavy fuel consumption.

Not cheap to buy but very easy to replace.

Re other checks....have you taken out the spark plugs and looked at them...they should all be the same colour....if you have an odd one out, ie its darker or wet, then thats where your problem lies...ie bad injector etc, plug lead etc.

Secondly when new plugs were put in were they the correct ones and have they been gapped correctly?

Lastly, and often over looked.....check you fuse box....take out each fuse and give it a clean at both ends with some emery paper...do the same on the fuse conectors and also check the condition of the fuses themselves. Its amazing how a bad contact can create intermitent faults

Lastly.........Good luck!

Gyri

Thanks MJ,
The MAF was checked in the MB garage with their computer and they said it's ok. But then, I also figured that when they are faulty, the signs could show up only at certain air density and temperature. How do I have this checked? I did a visual check a couple of weeks back and found that the Film (this doesn't have a coil, but a flat sturdy film, like a green circuit board strip with etched metal) looked perfectly clean and no pittings. I have been changing the air filter (stock) in regular intervals despite it not being dirty most times. The car has run just 41,000 Kilometers.
The spark plugs were replaced 400Km back as part of the general service. I'll check the lead wires to the plugs. Elsewhere I read that (for the E series) it's advisable to change the ignition coils (presumably in-expensive) during spark plug changes. I am going to check the prices for that.
I have installed multi point Bosch spark plugs, which pick the ideal spark gap automatically depending on the resistance required, no manual adjustment possible here. They aren't anything special like "platinum" or so.
Thanks for also pointing out the "fuse" check, something that trivial could always cause quite a hazzle. Will run though the cleaning as suggested by you.
The one thing that still bothers me is that, the symptom doesn't appear like an engine mis-fire (as in an electrical problem), but then who knows what and how problems manifest with all the sensors and control circuits in this car.

mjtray

Re the plugs.....MB's run best on standard plugs....are multi point plugs standard on the 220?.....if not I would change them for a set of standard Bosch plugs and make sure you get the correct temperature range installed, ie as per your handbook, and make sure they are gapped correctly.

Re your MAF....hard to diagnose if its just starting to fail.....it would start to throw up codes on your ECU though.

Good idea to check the coil packs....on my old M104 engine, which also had coil packs, the connector that goes from the coil pack to the plug can crack if it has not been removed carefully...check this.

Coil packs for my M104 were not cheap...connectors on the other hand were cheap to replace.

Good luck

Gyri

I had standard plugs ( single, regular point) b4 the last service. The same symptom existed even then. That's the reason I haven't changed them back. But then, I plan on doing so the next time I visit the spares dealer. Have to eleminate all the doubtful elements.
Regarding the MAF, the ECU was read for fault codes and it did not show an error, atleast that's what MB men told me.
I hope I'll get some time tomorrow to work on the vehicle, will clean up the fuses and their respective holders, as the first order of business.

Thanks!

Gyri

A wise man somewhere in one of the forum topics mentioned that if someone nails their problem, the least they owe the folks on the boards is to mention the details that helped solve their issue(s). I agree, as there are many topics that end without a note on whether the problem was solved or not. SO,

I changed the throttle body (~ USD380) and this solved the problem. I have driven the car (about 200 KM) in various conditions since, hot weather, early mornings, rainy conditions, heavy traffic and long highway cruises, no idling problems, no hesitation during acceleration, no stalling. It took me 45 minutes to change the throttle body. Should take less for an experienced DIY. Just remember to disconnect battery before attempting this. One problem I faced was that an "o" ring was missing in the interfacing area with the casted-metal inlet manifold. Unfortunately, I didn't have a spare one and had to use high temperature RTV sealant in that area. Apart from this, I had some resin coated fibreglass sleeve, which I used to wrap the throttle body’s connector cable, and secured the same with heat resistant adhesive tape. This is purely a precautionary measure to prevent the cable from turning brittle from heat again.

For all W124 owners, I strongly recommend that they check their wiring harness during all service routines. If found brittle or damaged, replace them. They are expensive (~USD 700, the lowest I have found so far) and the MB people might charge stiff on labour. If you want to do it yourself check
http://www.mercedesshop.com/wire_har...20_harness.htm
. One thing to consider while changing is that the new wiring harness might not be of a better grade, so it too could go bad in 40000 kms or so. Hence, before changing, as suggested above, wrap the wires with resin coated fibreglass sleeves of suitable diameter and secure them with high temperature adhesive tapes. Don't go over-board and wrap them too much as they might end up not being flexible enough to go through all the bends. Bad wiring harness spoils many electronic components such as sensor and actuators long before the shop-computer can properly diagnose them.
Here is another suggestion for those owning a W124 with HFM fuel management system and unhappy with the info available on Haynes W124 manual or MBOA W124 manual. Buy the Haynes C-class 1993-2000 manual. The engines covered in this manual are HFM type and hence give you more related information.

I really would like to thank all you folks for your suggestions and also for the various topics that have already been posted earlier.

mjtray

Good to hear the feedback and that you have got your problems fixed.

So it was a new throttle body.....I can only but think that the original must have been defective from the start and that it got gradually worse over time