MAF testing / voltages
Thread Starter
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Joined: May 2017
Posts: 257
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W209 CLK55 - 2003
M113 Rough idle and MAF testing
My 2003 CLK55 is showing P2017 and P2086 codes and has just started stuttering very slightly on braking.
To me that is something related to air metering across both banks and potentially a MAF fault.
I have an iCarsoft i980 code reader and read online that voltage is one way of telling that the MAF is working or not. I think the i980 describes this as HFM-SFI voltage and my car is reading 1.00v.
From what looks like Mercedes:
intake air temperature [0…40] C: signal voltage [0.980…1.030] V
intake air temperature [40…60] C: signal voltage [0.990…1.040] V
intake air temperature [60…80] C: signal voltage [1.000…1.050] V
I guess my question is, how reliable are tools like the i980? I am slightly suspicious that it is reporting a perfectly rounded number, although it is within the range.
To me that is something related to air metering across both banks and potentially a MAF fault.
I have an iCarsoft i980 code reader and read online that voltage is one way of telling that the MAF is working or not. I think the i980 describes this as HFM-SFI voltage and my car is reading 1.00v.
From what looks like Mercedes:
intake air temperature [0…40] C: signal voltage [0.980…1.030] V
intake air temperature [40…60] C: signal voltage [0.990…1.040] V
intake air temperature [60…80] C: signal voltage [1.000…1.050] V
I guess my question is, how reliable are tools like the i980? I am slightly suspicious that it is reporting a perfectly rounded number, although it is within the range.
Last edited by breeze247; Dec 23, 2020 at 12:38 PM. Reason: MAF did not fix it! Title change.
Thread Starter
Senior Member
Joined: May 2017
Posts: 257
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W209 CLK55 - 2003
Just to close this out and for the benefit of others, I replaced the MAF with a genuine new Bosch unit.
Massive improvement, smoother running and feels like the car is making more power. Engine speed is more stable, particularly at idle where it was varying quite a bit. I also found that the jerkiness that I had when coming off the gas has gone. It was so bad that I had assumed there was an issue with the engine/transmission mounts or even a propshaft flex disc.
On the i980, I would say that it is good enough to tell you that a MAF is present, but probably not enough to tell you, from the live data, that it is at fault. Regardless, codes wiped and they have not returned.
Massive improvement, smoother running and feels like the car is making more power. Engine speed is more stable, particularly at idle where it was varying quite a bit. I also found that the jerkiness that I had when coming off the gas has gone. It was so bad that I had assumed there was an issue with the engine/transmission mounts or even a propshaft flex disc.
On the i980, I would say that it is good enough to tell you that a MAF is present, but probably not enough to tell you, from the live data, that it is at fault. Regardless, codes wiped and they have not returned.
Thread Starter
Senior Member
Joined: May 2017
Posts: 257
Likes: 31
W209 CLK55 - 2003
Bouncing this back up...
I fitted the new MAF and the car ran very well for a short period.
It then started doing exactly the same things as before; rough idle and generally feeling a bit down on power.
I think replacing the MAF just stopped it being used as an input for a short period, and the car used a default map for fuel that was linked to throttle position or engine speed.
So I am back to square one, with a brand new MAF.
My thinking is that there is an air leak downstream of the MAF. Both banks showing the same fuel trim issue means it has to be in the intake manifold or the pipes around it, right?
Thoughts? I recently did valve cover gaskets and replaced all the spark plugs. As part of that I resealed the breathers and replaced all 4 of the breather pipes from the valve covers. I had the issue before that, so no change there.
The MAF appears properly seated.
The car does get slightly better when warm.
I am wondering whether the intake manifold needs to be removed. Or perhaps a smoke test?
I fitted the new MAF and the car ran very well for a short period.
It then started doing exactly the same things as before; rough idle and generally feeling a bit down on power.
I think replacing the MAF just stopped it being used as an input for a short period, and the car used a default map for fuel that was linked to throttle position or engine speed.
So I am back to square one, with a brand new MAF.
My thinking is that there is an air leak downstream of the MAF. Both banks showing the same fuel trim issue means it has to be in the intake manifold or the pipes around it, right?
Thoughts? I recently did valve cover gaskets and replaced all the spark plugs. As part of that I resealed the breathers and replaced all 4 of the breather pipes from the valve covers. I had the issue before that, so no change there.
The MAF appears properly seated.
The car does get slightly better when warm.
I am wondering whether the intake manifold needs to be removed. Or perhaps a smoke test?
Last edited by breeze247; Dec 23, 2020 at 12:46 PM.
Out Of Control!!
Joined: Sep 2018
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From: unbegrenzt
2017 GLE350 4MATIC
Fuel spark, air and sensors.
spark: plugs, wires and coils
fuel: pump, regulator, injectors
air. pcv, intake
sensors: MAF, O2, throttle position, accelerator position, cam position, crank position, water temp
Does the rough idle smooth out from a cold start to when the engine warms/thermostat opens?
I would double and triple check the work you did on the breathers.
Is there any smoke or steam coming from the tailpipe?
spark: plugs, wires and coils
fuel: pump, regulator, injectors
air. pcv, intake
sensors: MAF, O2, throttle position, accelerator position, cam position, crank position, water temp
Does the rough idle smooth out from a cold start to when the engine warms/thermostat opens?
I would double and triple check the work you did on the breathers.
Is there any smoke or steam coming from the tailpipe?
Thread Starter
Senior Member
Joined: May 2017
Posts: 257
Likes: 31
W209 CLK55 - 2003
Fuel spark, air and sensors.
spark: plugs, wires and coils
fuel: pump, regulator, injectors
air. pcv, intake
sensors: MAF, O2, throttle position, accelerator position, cam position, crank position, water temp
Does the rough idle smooth out from a cold start to when the engine warms/thermostat opens?
I would double and triple check the work you did on the breathers.
Is there any smoke or steam coming from the tailpipe?
spark: plugs, wires and coils
fuel: pump, regulator, injectors
air. pcv, intake
sensors: MAF, O2, throttle position, accelerator position, cam position, crank position, water temp
Does the rough idle smooth out from a cold start to when the engine warms/thermostat opens?
I would double and triple check the work you did on the breathers.
Is there any smoke or steam coming from the tailpipe?
I was a bit stumped but thought now it is fixed it was worth sharing the solution for the benefit of others.
In summary:
- MAF was bad
- MAF was replaced but I did not fit it properly and there was an air leak
- Car ran fine for a short period, I guess because there is a window for adaptation, and then became hesitant again, this time much worse.
- I found the intake leake and fixed it. Problem went away.
If anybody is curious, it was one of the rubber fittings around the base of the MAF. Unmetered air because it was after the MAF.
It has been fine for a while now.
Last edited by breeze247; Aug 19, 2021 at 02:30 AM.
