Rough idle
11-30-2021, 09:50 PM
#1
Rough idle
I have a 2015 c300 with about 105k miles. When at a full stop or in park my car doesn’t have the smoothest Idle. Some may not notice it but I defiantly can. Just little hiccups nothing major. Anyone know what this could be? I replaced 2 fuel injectors, all ignition coils and all the spark plugs a couple months ago because I was having a misfire issue but car has been running fine since then. Any guidance would be appreciated.
Last edited by Hello32; 11-30-2021 at 09:55 PM.
12-02-2021, 12:00 AM
#2
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MY'14 W212 M276 3.5NA @60kMi
plugged Lambda...
Just replace your primary Lambda-O2 sensor. This causes your idle mixture to be off by a little.... busted PCV air leak can help screw that up too.
Last reset the ECU to speed up relearning the mixture map, specifically idle. After that your engine will have smoother low rpm torque again.
Last reset the ECU to speed up relearning the mixture map, specifically idle. After that your engine will have smoother low rpm torque again.
Last edited by CaliBenzDriver; 12-02-2021 at 04:45 AM.
12-02-2021, 03:59 AM
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MY'14 W212 M276 3.5NA @60kMi
both upstream only
You'll need to use a scanner to reset the ECU. Once you got the sensors replaced, leave them disconnected. This will trigger couple ECU errors that you'll be able to reset. That will cause ECU to relearn mixtures using the new sensors you will have then connected.
12-02-2021, 04:52 AM
#6
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MY'14 W212 M276 3.5NA @60kMi
check running voltage...
Check your running voltage is around 14.4v and float your battery overnight.
This will temporarily rule out unregulated low voltage.
This will temporarily rule out unregulated low voltage.
12-02-2021, 08:38 AM
#7
both upstream so they read the same as close as possible to each other.
You'll need to use a scanner to reset the ECU. Once you got the sensors replaced, leave them disconnected. This will trigger couple ECU errors that you'll be able to reset. That will cause ECU to relearn mixtures using the new sensors you will have then connected.
You'll need to use a scanner to reset the ECU. Once you got the sensors replaced, leave them disconnected. This will trigger couple ECU errors that you'll be able to reset. That will cause ECU to relearn mixtures using the new sensors you will have then connected.
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12-02-2021, 12:09 PM
#8
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MY'14 W212 M276 3.5NA @60kMi
yes, exactly. Downstream O2 are just checking the cats efficiency. Unrelated to your problem.
The upstream sensors directly feedback to the fuel injection control. They get partially plugged up and partially fail without code because their reference output is still indicative.
Make sure your scanner can interact with the ECU module before you trigger faults mentioned above (Just saying: don't cause faults if you have no tool to reset ECU).
The upstream sensors directly feedback to the fuel injection control. They get partially plugged up and partially fail without code because their reference output is still indicative.
Make sure your scanner can interact with the ECU module before you trigger faults mentioned above (Just saying: don't cause faults if you have no tool to reset ECU).
Last edited by CaliBenzDriver; 12-02-2021 at 12:21 PM.
