2003 C320 running rough
 

The last few drives in my wife's 2003 C320 I noticed it was running rough.


I picked up a big bottle of Lucas fuel treatment and filled up the car with Super.
She told me not to put super because it cost more.
I found out she has been putting regular gas in the car for a year.


I fussed at her and blamed the cars condition on low octane fuel.
We ran out the interstate for 40 miles and back at about 75. When we got back it seemed to idle better, but it seems to want to stall at take off.


Any ideas

Your engine mounts or transmission mount is probably shot. The m112 engine is perfectly capable of running smoothly on 87 octane without any damage. The only down side is slightly reduced peak power. The stalling is a symptom of a weak fuel pump.

How many miles are on the plugs? I see dirty throttle bodies cause the almost stalling when coming to a stop symptom.

Better buy her something good for Christmas, regular fuel won't cause a rough idle. About all that will happen is a slight reduction of max power due to ignition timing reduction. At part throttle you won't likely notice a difference.

I would personally retract that statement. x2 on the motor mounts. Could be plug wires/connectors/plugs also I suppose depending on the age of those.