Rough Running A170

[Bob India]

Hi Everyone,

I would be grateful for advice regarding my 2005 A-Class (W169). 40,000 miles on the clock. I bought it new so mileage is correct.

Symptoms are; Intermittent rough running and car shakes.
The car starts OK, then it's like one or two of the cylinders are turned off and the car starts to shake. Then a few seconds later it's OK again. This process keeps happening every few seconds, (Between 5-10 seconds intervals) and is getting worse. This happens up to around 40mph, then going above this speed, say around 50mph and above, the car seems OK. Also, I can't seem to do more than 70mph, the engine tops out at about this speed.

I'm guessing the ECU is switching something ON and OFF and cycling depending on a reading it is getting from some sensor..

I went to my local NON Mercedes garage and they used a LAUNCH code reader which gave its reading as codes ;

00F6-008 Plausibility check of values for components B28(Pressure Sensor) and M16/6(Throttle valve actuator) in idle and under partial load Lambda control OK.

00F6-004 Plausibility check of values for components B28(Pressure Sensor) and M16/6(Throttle valve actuator) in idle and under partial load Lambda control OK.

Given the symptoms and the diagnostics codes I have been given with the explanations, does anyone know what the problem is or where or what I should be changing?

I would appreciate help from those who have had similar issues and what was done to resolve the issue. I do most of my own car repairs so familiar with most aspects of repair.

Does anyone know what B28(pressure sensor) & M16/6(Throttle valve actuator) are? I have an idea of what the Throttle Value Actuator is but would welcome comments from all those who Actual know and/or have had this problem sorted and how..

Many thanks..

Robert

 

[Wighty]

Where abouts do you live Bob in case there is a decent MB Indy that someone can recommend nearby that can use the MB Star computer to read the cars faults .
Did your garage not have suggestions on what needs looking at/changing ?

 

[bembo449]

is this a diesel engine then ? at that miles its bound to be something blocked or caked up through lack of use ?

 

[alexanderfoti]

No, W169 A170 is a petrol.

Bob, if you are local, we could take a look. Those code definitions do not make much sense. Ideally it needs to go on STAR diagnostics.

 

[Bob India]

Where abouts do you live Bob in case there is a decent MB Indy that someone can recommend nearby that can use the MB Star computer to read the cars faults .
Did your garage not have suggestions on what needs looking at/changing ?

I live in West London, Uxbridge way. I borrowed a comprehensive LAUNCH code reader. The garage would not commit themselves as to what it was as they were not gonna do the work and not a Mercedes Garage. They can only go on what their code reader indicated.

I have no experience of the STAR diagnostics.. Will it give any more detail than the LUNCH reader. As far as I am aware, both will just read the stored codes? Will it test each component individually?

From what I know, the codes are pointing to the Manifold pressure sensor, or Throttle body. One of them is generating an error.

I have sourced a NEW Patten part, Throttle assembly from Germany. I will be getting hold of the car from my daughter, later this week and will try in sequence to;

- check for vacuum leaks
- fit new air filter,
- clean the throttle unit,
- check the wiring to the Manifold sensor
- Test Manifold sensor and change if necessary
- fit new throttle body assembly.

I suspect something is advancing or retarding the timing and the ECU usually gets inputs from the Throttle Position sensor, MAF, and Manifold sensor and adjusting as necessary?

Yes, the car is a 1.7 Petrol Engine.

Any suggestions welcomed..

Thank You

Bob.

 

[Wighty]

Your nearest Indy that is regularly on the site is Ian at Start Mercedes in Reading that is highly respected , he will obviously use Mercedes Star to diagnose faults .
I get that you would want to check and diagnose things yourself , I would and do myself with an icarsoft MB2 reader (Merc specific) . I would avoid buying any high price parts unless I was very sure they were at fault .
Bear Ian in mind for a Star session even if you then use that to conduct your own repairs ? (Unless of course your plans/repairs work out)
Good luck either way

 

[mattkh]

Is it a Automatic gearbox car?

 

[Bob India]

Your nearest Indy that is regularly on the site is Ian at Start Mercedes in Reading that is highly respected , he will obviously use Mercedes Star to diagnose faults .
I get that you would want to check and diagnose things yourself , I would and do myself with an icarsoft MB2 reader (Merc specific) . I would avoid buying any high price parts unless I was very sure they were at fault .
Bear Ian in mind for a Star session even if you then use that to conduct your own repairs ? (Unless of course your plans/repairs work out)
Good luck either way

Thank you.. I will have a go first before spending too much money.. Try the simple stuff first. My only issue is I have to work in the garden as I don't have a garage and the weather is gonna be cold this week..

Yes, the Car is an Automatic..

 

[Wighty]

Thank you.. I will have a go first before spending too much money.. Try the simple stuff first. My only issue is I have to work in the garden as I don't have a garage and the weather is gonna be cold this week..

Yes, the Car is an Automatic..

I know what you mean about working outside , that's why I always schedule my breakdowns for warm weather

 

[Bob India]

OK. Today I took out the throttle body. It was filthy and old and brown gunk contaminated. I have cleaned it up and the blocked breather pipe that comes from the engine. It was pretty much blocked up. Using my personal small Code reader and the torque app on my phone, I was getting codes P0068 and P0351. Now i have reassembled the Throttle body, the P0068 code is no more, but the intermittent rough running is still there and code P0351 is still present.

I understand this is referring to cylinder no 1, Coil or Spark plug or lead, or Powertrain ECU. I will attempt this tomorrow. I would welcome any constructive comments and methods for diagnosis.

Also, am I correct in thinking there is one large coil unit and not individual coils on each spark plug... ?

Thanks in advance..

Bob.

I will be posting my photos of the throttle body to show the condition it was in..

 

[mattkh]

I am following this with great interest. Look forward to the photos.
Right, when you took the throttle body out, did you see the MAF (Mass Air Flow) sensor tips. If not, I suggest you look for it, and give it a clean (after researching how to), especially as you say the throttle body was very mucky.
On my car, the ignition coil is a long 4 legged coil.
Also, check the wires going to the 'pre-catalytic-converter' Oxygen sensor.

 

[Bob India]

I am following this with great interest. Look forward to the photos.
Right, when you took the throttle body out, did you see the MAF (Mass Air Flow) sensor tips. If not, I suggest you look for it, and give it a clean (after researching how to), especially as you say the throttle body was very mucky.
On my car, the ignition coil is a long 4 legged coil.
Also, check the wires going to the 'pre-catalytic-converter' Oxygen sensor.

Hi Mattkh,
I note you have Chassis W168. I have the W169 chassis. In 2005, the A-Class has a face lift and engine modification. The engine in my car is the one being used in the B-Class.

I phoned Mercedes, and asked them about the MAF. They told me my engine does not have a MAF, but a Pressure Sensor which is positioned on the left side of the Air Intake tubes. The way cars with MAFs are usually organised; The MAF is positioned at the beginning of the Air Intake Path, then Air Filter and Air Filter Box, then Throttle Body. My car has the Air Intake tube, going to the Air Filter and Air Filter Box, then Throttle Body, then Air Intake Temperature Sensor. (Not to be confused with a MAF. This engine has no MAF). I did not clean the Air Intake Temperature Sensor. After cleaning the throttle body, there is no more Throttle or pressure sensor error code.

As for the ignition coil. You say yours has 4 legs for the spark plugs. On my engine, I had a look and found I have two Coils. I will be swapping them over and see if the faults moves to the other cylinder. That way I will know if the coil is actually at fault before replacing it.

Thanks

Bob.

 

[Bob India]

PHOTOGRAPHS

 

[Bob India]

This is an image of the Diagnostics screen from the Launch Diagnostics scanner.

I was so fixated on the first two errors, thinking these were the cause of the bad engine running, that I totally missed the next error code; "The Ignition duration of the spark plug at Cylinder 1 is too short [P0351]"

This is the actual reason for the bad engine running and shaking. If I had fixed the P0351 error which I think is Coil Pack A fault, or Lead, or spark plug or Power Train Control Module, FIRST, the engine may have started to run better. However, you can see the condition the Throttle body was in and needed cleaning to clear error code P0068 as well, which I am glad I did.

 

[ZZZZ]

Great result, thanks for posting the pics and description.

One thing though - the W169 is not a facelift, it's a different model from W168.

Both models did have facelifts - W168 in 2001, and W/C169 in 2008, but these were within the same model designation (as all other Mercedes facelifts). When looking up parts in EPC, or checking WIS pages for a particular job, the facelift is determined by either a MY, or a year code (if mentioned), and the last six digits of the VIN / FIN.

 

[mattkh]

I phoned Mercedes, and asked them about the MAF. They told me my engine does not have a MAF, but a Pressure Sensor which is positioned on the left side of the Air Intake tubes.Bob.

Thank you very much.
In that case, on your engine, this sensor must be telling the ECU how much petrol to send to the cylinders. It may be a good idea to clean this sensor as well, with a carburetor cleaner. If you do then please up a picture of the before and after. Thanks.

 

[Bob India]

Todays mission was to swap the ignition coils with each other and see if the error code moved from cylinder 1 to cylinder 3. This would indicate the coil was faulty. This was a Mission and a half. Removed air filter box and Throttle body AGAIN. Part Removed the metal braket holding up the Air Tubes to get access to the coils. The coils have a Torx screw in the middle holding it against the engine. After removing the coils one at a time, MAKE SURE you know which output port feeds which cylinder.. LABEL THEM. There is nothing worse than getting the leads in the wrong way round and introducing more errors and troubleshooting. The leads themselves are labeled by Bosch at the spark plug end. Each coil feeds two cylinders. Left one is Bank A for cylinders 1 & 2, Right Bank B is for cylinders 3 & 4. I am currently getting error [P0351]. By swapping the coils over, I was expecting to see error [P0353], indicating the fault had moved to cylinder 3. This would confirm the coil is faulty. A new coil costs £154+Vat from Mercedes. They do a reconditioned one for £77+Vat but you have to give in your old one as Part Exchange. So this procedure is a good way to confirm if the coil is faulty and not fork out for a new coil if it's not needed.

The hard part is removing the leads from the coil as you can't get a good grip to pull the leads off. Pull the leads off the spark plugs, take out the coils and then remove the leads from the coils. This was relatively easy from cylinders 2, 3 & 4 but an absolute "BITCH" from cylinder 1. It refused to move. I could hear the cap inside the lead come away, but the lead refused to come off the spark plug. In the end, repeated tugging progressively harder, pulled the lead off. The problem was the rubber in the lead was so tight on the plug.

I labeled the coils and cleaned up the underside with a wire brush, just in case there needs to be metal to metal contact for earthing reasons. But I doubt this is needed. Better to be safe so just do it.

I swapped the coils over and refitted the throttle unit and then loosely fitted the Air Box and top cover.

I cleared the error from the ECU. Started the car and waited for the error to reappear. And it did !! But to my dismay, I had the same error [P0351]. This meant both coils were OK.

What now ? The problem must be either before the coil or after the coil. I removed the number 1 cylinder spark plug. The Plug looked OK, but the gap did look a bit big. I decided to change all the plugs. Bought new ones. The gap on the new ones did look less, but I could not check and compare as I could not find my feeler gauge !! New plugs went in, cleared the error on ECU, loose fitted the Air box again and started the car. Engine sounded OK. Then went rough again, for a few seconds then cleared again. The constant cycling from smooth to rough at low idle had gone. Had I finally sorted the error ? I reassembled the parts and took the car for a long Test drive. It all looked good. There was an occasional rough spot but it cleared in about 3 seconds each time. I'm thinking it was the spark plug all along. I parked the car. Later I went out again for another drive, and all of a sudden, the problem was back. DAM...... Not as bad as last time but definitely there and the Check Engine light came back on..

The car belongs to my daughter and she has taken it now as it is. I will get it back at the weekend when I will try the next step, which is Change the Ignition lead to cylinder 1, then check wiring on the other side of the coil. And the saga continues !!

Some Pics from todays endevours.

 

[mattkh]

Thank you for the pics.
Ring your daughter to put a bottle of 'injector cleaner for petrol engines' in the fuel tank. If she does a good mileage regularly during the week, that will rule out a sticky injector.

 

[Bob India]

Thank you for the pics.
Ring your daughter to put a bottle of 'injector cleaner for petrol engines' in the fuel tank. If she does a good mileage regularly during the week, that will rule out a sticky injector.

Have tried that already with 4 doses of Redex from one bottle. Didn't seem to help..

 

[mattkh]

Your thread has been very useful in educating me.
One video on youtube was saying that the 1 in p0351 refers to ignition coil 1. He said it can also mean that the connection to the coil is dodgy. So, when you get the car, clean and check the connector.
In my research for which I have to thank you again, the duration of the spark is a feature of the current going through the primary winding. So increased resistance due to corrosion at the connector pins is likely.
When you take the plug leads out, you can also compare the resistances of the leads to see if there is any difference.