[Photodude]

M113 engine, ME 2.0

What could cause MAF sensor reading to go high at idle like 24, 28… 40 Kg/hr, where it should be 16 (14-18, 10-20 max), other than faulty MAF sensor? The reason I say other than… because MAF is brand new, from MB dealer installed two months ago.

Also, this is third MAF in like two years and symptoms (or diagnostic data) looked similar. I’m starting to think that I may be barking at the wrong tree.

In my prior experience with this, bad MAF would read low (under reporting air mass), vacuum leaks could cause readings in that direction also… idle speed adaptations going high on the + side. So you always check for air leaks before going farther.

This is going opposite direction, adaptations going south, on the minus side. Vacuum leaks couldn’t cause that, could they?

I’m trying to rock my brain what I could test before I take the car to the dealer, for warranty claim on that MAF sensor they sold me.

 

[Ken S]

It is curious indeed, but maybe it's not just the aftermarket that is struggling to produce reliable MAF sensors.
Perhaps OEM's are now having some of the same issues?
Possibly due to supply chain issues and having to use important materials from different suppliers.

If you are confident that the plug connection is very clean and in good condition, I suggest that you see how open they are to a warranty request.

 

[brauhaus]

Are you testing idle readings with the car fully warmed up and with all accessories off? How's the gasket between the neck of the intake housing and the MAF housing?

 

[Photodude]

If you are confident that the plug connection is very clean and in good condition, I suggest that you see how open they are to a warranty request.

I’m not confident about anything at this point. The way Mercedes warranty on parts works (purchased from the dealer and self installed), … If you think the part is defective, you need to bring the car to the service department (with the part installed) and let them determine if the part is defective. If it is they will replace it free of charge, installation included. If they determine otherwise, you are on hook for whatever they charge for diagnostics.

I’ve done this before, including MAF, and they came good but you better be 100% sure about you diagnosis. This could be tricky with MAF. Otherwise they will be more than happy to prove you wrong and take your money.

 

[Photodude]

Are you testing idle readings with the car fully warmed up and with all accessories off? How's the gasket between the neck of the intake housing and the MAF housing?

Yes engine fully warmed up, coolant and oil at operating temps, A/C off. MAF gasket is new.

I had P0170 code, idle speed self adaptations at limit value. I was checking actual values at idle and indeed adaptations were almost at the + limit on both banks (0.9 ms) with the right side slightly higher and going over +1 ms limit, hence the code stored. Air Mass was on the low side of the idle speed range. This would be consistent with vacuum leaks, among few other possibilities.

I cleared the code, went back to look at the live data again and within few seconds I noticed this surge in Air Mass going from 12 Kg/hr to 16, 20, 24, 28… back to 24, 20, 24… and it would stay there, while RPM did not increase albeit idle was slightly rough. Self adaptations went the other way, down to - 0.5, -0.6 ms. After 10-15 minutes nothing changed so I shut it off.

Drove the car today, several short trips. When I connected SDS this evening to see what’s going on, no codes but adaptations are back to high plus (+0.7, +0.9 ms) without crossing the limit. Air Mass down in low part of the range (12 Kg/hr). What does this all mean, I’m not sure just yet. Was this sudden surge in Air Mass values one of incident? I doubt it but, it’s difficult to tell unless I drive with scanner connected for extended period of time.

It’s pretty obvious to me, looking at the live data that I need to check for air leaks regardless of anything else that might be going on there. That said, what could possibly push MAF values up? Other than flaky sensor or electrical connector, maybe?

 

[brauhaus]

It’s pretty obvious to me, looking at the live data that I need to check for air leaks regardless of anything else that might be going on there. That said, what could possibly push MAF values up? Other than flaky sensor or electrical connector, maybe?

Bad wiring, which may or may not be a problem at the connector. Test resistance at the connector pins.

 

[Photodude]

Quick update. I drove the car with the scanner connected looking mainly at fuel trim values (hate that term) and air mass, then switched to SDS laptop and flipped between air mass, idle and partial load adaptations… while the surge in air mass values (at idle) is not one of and is not normal, quite clearly this is not what’s causing the codes to come on.

The codes (P0170, P0173) indicate idle adaptations hitting the limit on the plus side. This can only be caused by vacuum leaks, bad MAF… few other but less likely factors. I know this is pretty boring but, I’m just thinking out loud… and when I look at the live data, relation between different parameters etc. It’s actually quite interesting to analyze this in real time.

Anyway I checked for air leaks, with smoke and found some at intake manifold gaskets. I’m not convinced they are significant enough to cause adaptations to go over the limit, there could be other factors, but I am convinced these leaks will not go away and are likely to get worse with time.

So my preliminary conclusion, given the history of my intake manifold… had been off twice in an attempt to re-seal it… I need brand new intake manifold in order to achieve proper seal.

 

[brauhaus]

The leaks are where the top and bottom halves of the manifold are sealed, or at the gasket between the intake manifold and cylinder head?

Replacing the manifold isn't that hard if you want to DIY. A new manifold is about $1k though.

 

[Swany]

Quick update. I drove the car with the scanner connected looking mainly at fuel trim values (hate that term) and air mass, then switched to SDS laptop and flipped between air mass, idle and partial load adaptations… while the surge in air mass values (at idle) is not one of and is not normal, quite clearly this is not what’s causing the codes to come on.

The codes (P0170, P0173) indicate idle adaptations hitting the limit on the plus side. This can only be caused by vacuum leaks, bad MAF… few other but less likely factors. I know this is pretty boring but, I’m just thinking out loud… and when I look at the live data, relation between different parameters etc. It’s actually quite interesting to analyze this in real time.

Anyway I checked for air leaks, with smoke and found some at intake manifold gaskets. I’m not convinced they are significant enough to cause adaptations to go over the limit, there could be other factors, but I am convinced these leaks will not go away and are likely to get worse with time.

So my preliminary conclusion, given the history of my intake manifold… had been off twice in an attempt to re-seal it… I need brand new intake manifold in order to achieve proper seal.

Just curious if at idle when you're seeing the MAF air mass readings changing are you also monitoring the throttle position? I'm wondering if the there's some changes to the throttle position to maintain the desired idle RPM. Assuming the MAF is okay, the changes to the air mass flow readings at idle would mean a vacuum leak that's not consistent and varying, which is possible but less likely and why I'm wondering if there's any changes to the throttle position when you're seeing this changes in air flow.
Some other potential air/vacuum leak sources in the intake manifold is the vacuum line up front controlling the intake flaps or the brake booster line into the rear of the intake manifold, there's an o-ring sealing the tube inserted into the manifold. This brake booster line is also hard plastic tube going into the intake manifold and can become cracked or broken in half, which I did break in my car when I used the brake booster tube as a hand brace while doing some work on the engine. When you did the smoke test did you check where this line where it enters the manifold?
Because you've changed the MAF and are still seeing similar problems as before I'm leaning more towards a vacuum leak but with the readings you're seeing it seems like it would only make sense if the leak was varying to some degree or if there's any throttle position changes, which is possible and one reason you turn off the A/C when looking the data. Slight throttle position changes are done by the engine control module to maintain the idle speed when the A/C clutch is turned on and off.

 

[Photodude]

The leaks are where the top and bottom halves of the manifold are sealed, or at the gasket between the intake manifold and cylinder head?

Replacing the manifold isn't that hard if you want to DIY. A new manifold is about $1k though.

The leaks appear to be at both gaskets between manifold bottom and cylinder head.

4 years ago I had the seal between top and bottom half re-done, this part is actually holding well so far. Gaskets at the cylinder head had to be reinforced with silicon back then, because there were questions about integrity of manifold surface at the gasket contact. It worked OK up to this point but, cracks appear to be forming… which is why I don’t think I can re-use this manifold when it comes off.

 

[Photodude]

Just curious if at idle when you're seeing the MAF air mass readings changing are you also monitoring the throttle position? I'm wondering if the there's some changes to the throttle position to maintain the desired idle RPM. Assuming the MAF is okay, the changes to the air mass flow readings at idle would mean a vacuum leak that's not consistent and varying, which is possible but less likely and why I'm wondering if there's any changes to the throttle position when you're seeing this changes in air flow.
Some other potential air/vacuum leak sources in the intake manifold is the vacuum line up front controlling the intake flaps or the brake booster line into the rear of the intake manifold, there's an o-ring sealing the tube inserted into the manifold. This brake booster line is also hard plastic tube going into the intake manifold and can become cracked or broken in half, which I did break in my car when I used the brake booster tube as a hand brace while doing some work on the engine. When you did the smoke test did you check where this line where it enters the manifold?
Because you've changed the MAF and are still seeing similar problems as before I'm leaning more towards a vacuum leak but with the readings you're seeing it seems like it would only make sense if the leak was varying to some degree or if there's any throttle position changes, which is possible and one reason you turn off the A/C when looking the data. Slight throttle position changes are done by the engine control module to maintain the idle speed when the A/C clutch is turned on and off.

Yes the throttle position changes with the airflow fluctuation. At idle, I’m reading 0.9-1.6 degree or 1-2% with air mass near the low end of the range. I did spend about 15-20 minutes with the smoke machine, looking everywhere… the only place I’ve seen smoke was on both manifold gaskets at the cylinder head. Checked the purge valve for possible leak, with the vacuum pump… none found.

 

[brauhaus]

I have read of cases where throttle bodies develop play and display symptoms at idle similar to what you describe. Can't say I've heard it happening in our cars though.

 

[Swany]

Yes the throttle position changes with the airflow fluctuation. At idle, I’m reading 0.9-1.6 degree or 1-2% with air mass near the low end of the range. I did spend about 15-20 minutes with the smoke machine, looking everywhere… the only place I’ve seen smoke was on both manifold gaskets at the cylinder head. Checked the purge valve for possible leak, with the vacuum pump… none found.

Seeing any smoke in the manifold gaskets to cylinder heads area has to affect idle conditions, air flow isn't much through the throttle body at idle so any air leaks elsewhere will be bypassing the MAF. I am wondering why the MAF readings are varying so much at idle and why I asked about the throttle position changing. What's going on with the manifold gasket surface that you mentioned? Is the surface questionable on the manifold side or engine side? With new gaskets and a clean surface I wouldn't expect the intake manifold to cylinder head to have a problem with a good seal.

 

[Photodude]

Some variation in MAF readings at idle is normal, as long as it is within specified range. Now, according to Mercedes DAS that range for M113 is 10-20 Kg/h at idle. However in my experience, that should be closer to 14-18 Kg/h. In fact on my SL500, when everything is in order, I see air mass at 15-16 Kg/h. That is with A/C off and engine fully warmed up.

Air leaks will affect MAF air mass readings in a negative direction (at idle only). That is what I’m seeing most of the time, 12-13 Kg/h. This and idle adaptations high on the plus side is consistent with air leaks.

Air mass readings high above 20 Kg/h, which I noticed from time to time, can’t have anything to do with vacuum leaks IMO. What is causing this occasional surge I don’t know. It could be electrical issue with the wiring harness/ connector, like Brauhaus suggested. EGR maybe? But whatever it is, it’s swinging idle adaptations in the opposite direction to the minus side but, not far enough to cause problem just yet. In any case, as long as vacuum leaks are present, they have to be dealt with first.

The surface imperfections were on the manifold side of the gaskets. Silicon sealant on top of the gaskets didn’t work as well as I would have hoped. So here I am, 4 years later having to deal with this again. I should have bought new manifold back then but, got persuaded by my friend that we can salvage this one.

 

[brauhaus]

In any case, as long as vacuum leaks are present, they have to be dealt with first.

Highly agree.

 

[Photodude]

FCP Euro has M113 intake manifold on sale right now, $799. That’s as good a price as I’ve seen for some time. I ordered it and should be here next week.

 

[Photodude]

New manifold is here, time to install it and fix this annoying vacuum leak issue… that has been bugging me bit too long.

 

[brauhaus]

New gaskets?

 

[Swany]

New manifold is here, time to install it and fix this annoying vacuum leak issue… that has been bugging me bit too long.

Nice new manifold. I know you've installed the manifold before but just wanted to say how much guide pins(modified M8 bolts) help hold the intake manifold gaskets in place when I installed the manifold in my car. I cut off the heads of some M8 bolts to make the guide pins, but you can also use M8 studs or 5/16" round wood dowel to make the guide pins, really helps out with the install. Looking forward to hearing about the results with the new manifold.

 

[brauhaus]

Indeed. I used short threaded rods.