breeze247

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.

breeze247

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.

breeze247

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?

chassis

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?

breeze247

Apologies for not coming back on this chassis.

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.