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Old 09-25-2008, 11:28 AM
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Join Date: Oct 2007
Posts: 2
Thumbs up W210 E320 rough idle/ misfire

I am hoping someone can help.

2002 E320 wagon 4matic 76k miles

Rough idle. No CEL. Definitely missing, can feel vibration in cabin at idle.

Pulled the following codes:
P0303 - 3rd cyl misfire
P0171 - Lean left bank
P0174 - Lean right bank
P0300 - Multiple misfire
P0303 - 3rd cyl misfire

What's been done so far.

We ran the smoke machine for air leaks.
EGR stuck open - Replaced
Dipstick tube o-ring - replaced
Sealed a couple of small vacumm tube leaks.
MAS - removed and cleaned with CRC MAF cleaner
Swapped Coil pack, wires and plugs from Cyl 3 to Cyl 1.

Reset Codes, re-read codes, pulled P0112 IAT Sensor. Looks like the IAT is integrated into the MAF sensor.

In my mind I feel it is narrowed down to MAF sensor, plugs wires or Coil pack.

Hoping for some suggestions rather than throwing parts at it. Any suggestions?


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Old 09-25-2008, 11:43 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Most likely the MAF...

Of course the spark plugs are to be replaced at 5Years or 100K miles which ever comes 1st.
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Old 09-29-2008, 02:35 PM
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Join Date: Oct 2007
Posts: 2

Problem was bad plug wire. Initially the misfire code was Cyl 3 and random misfire. I moved the coil, wires and plugs to Cyl 1. Got too impatient for codes to show. Unplugged coil #1 without change to idle, replace those 2 wires, runs smooth.

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