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2004 CLK320 Poor fuel economy

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Old Jul 10, 2013 | 11:28 PM
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2004 clk320
2004 CLK320 Poor fuel economy

Good day to all. This is my first post. Have had the car for two years. Very happy, however, have noticed deteriorating fuel economy. Have replaced air filters, used an aggressive fuel additive and recently performed an induction service (de-carbonizing via vacuum line). No results. Thoughts welcome. -Al
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Old Jul 10, 2013 | 11:53 PM
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Sometimes a bad MAF sensor can cause fuel economy problems, yet not trigger an MIL.
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Old Jul 11, 2013 | 06:48 AM
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+1^. What mileage? Could be poor MAF or O2 sensors getting to the end of their life & cycling too slowly. You should ultimately get a fuel trim code but if the sensors are shot you wont.
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Old Jul 12, 2013 | 12:40 AM
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There was a huge improvement in MPG on my 08 550 after cleaning the MAF. Thanks to Rodney's sharing of knowledge, I could clean the MAF sensor without removing the housing.

There was no official "controlled environment" tests done, but my MPG (using the same route at differnt times) is consistently 1.5 - 2 MPG higher than before the cleaning.

I just spayed CRC MAF cleaner on the wire. I sprayed it through the mesh cover over the intake.

On start up, the engine seemed to "skip a beat" then settle in on a smooth cold start idle. Others would have to tell us what was going on with the "skipping a beat" - I am no so mechanically inclined - my guess would be the ECU resetting the fuel mix.
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