asian_xl

I am no mechanic, so let me try to explain what is happening here.

We bought a S320 few months ago knowing the ex-owner did not maintain it properly. Although the engine runs smooth, I still decided to change all filters and oil at a garage for long run.

1. Replaced the old leaky radiator w/ new and OEM fluid
2. Air/fuel/oil filter
3. Mobile 5w 40 (I live in Asia, this is what MB recommended)
4. OEM Tranny oil
5. Fixed some seals as I see several oil leaks
6. 12 Bosch platinum spark plugs (S320) OEM spec.
7. Tighten some exhaust bolts as it rattles during acceleration (it still rattles a bit nowaday)
8. OEM brake pads

When my dad drove it back home , he told me the car doesn't feel to be alright at stops. The engine starts shivering like an old engine, but runs fine at any speed. What could be the problem here? Could it be the spark plugs or oil?

wallyp

There are a lot of possible causes for the rough idle. Some include:
- The coil/plug wires could have been damaged during the plug change (or could have been damaged before).
- There might be a vacuum leak, perhaps from a brittle or loose hose. It is very easy to break an old hose when it is moved during repairs. You can sometimes find such a leak by using a 1,5 m rubber or plastic hose to listen for the hiss of a leak. One end in your best ear, the other end moved around the intake manifold and over the engine to pick up the hiss - stay away from moving and hot parts!
- Dirty, faulty or disconnected fuel injector.


There are other possible causes, but the oil is not at all likely to be a cause.

MJD

One of the biggest engine/vibration issues is the motor mounts. These mounts are liquid filled and typically only last about 60K miles before needing replaced. If your engine runs smooth through out the power band, then check the mounts. And replace all three mounts at once (both motor and transmission), it will feel like a new car.

Now if it is rough idling I would 2nd the plug wires being replaced as well, but if it is more of a vibration issue then mounts would be my first suspect.

tusabes

Sounds like something went wrong during the service

Spark plug wires probably not on right

ibeforreal

Did you replace the spark plugs wires when you replaced the plugs? If the old wires are not clicked on really tight on the plugs it will cause a slight mis-fire problem. Could also be a problem with the Mass Airflow Sensor (MAF) that is causing the shimmering when idling at a traffic light.

servicetech

Also recheck the spark plugs as sometimes it cracks during installation while you tightening it. it happened to me last year when I changed my spark plugs.wires also get damaged during the removal.

asian_xl

The rough idle only occurs when I stop the car completely, then I can feel the slight vibration coming from the steerting wheel and pedals, pretty much the whole car.

The car has 78000km on it, and NO Spark Plug wires were replaced as the mechanic said they are fine before handing us the key.




Also, 1/8 tank of the fuel just disappears after a week, I really need to bring the car back to the shop

tusabes

Wires are often improperly reinstalled