Hey guys,

Looking for a little bit of advice here. I recently purchased a vehicle from the company I work for (Enterprise Rent-a-car). I had a Mercedes dealership inspect the vehicle as well as a local shop my company uses. Both places gave the vehicle a clean bill of health.

However, recently I was driving the vehicle and while I was stopped at a stoplight the engine started to sputter and shake a little. The "Check Engine" light then turned on and the vehicle wouldn't go over a couple miles per hour. Luckily I was a block away from home and was able to coast in and call a tow truck.

The shop I brought my car to said the check engine codes were "misfires on cylinders 1 and 6." They said they believe it is dirty injectors. They put some injector cleaner in the tank and I'm still driving through what's left in the gas tank.

My question is, do any of you have any idea as to what may be causing my vehicle to idle rough and "shimmy" while i'm stopped or at a very low speed. It doesn't always get the shake, it seems to randomly happen.

***Note*** Just before the check engine light went off, the "reduce engine oil level" notification came on and then went away. Since that happened, I had the shop drain the oil and put 8 new quarts back in it. I don't know if that notification would cause what happened or not.

Any advice would be excellent. Service records from the carfax are as follows:

2001 C240 Sedan
101k Miles (Current Mileage)
109-Inspection and stardard maintenance done at time of purchase

100k Miles
Vehicle serviced at authorized Mercedes Dealer

96k Miles
Vehicle Serviced
Oil & Filter changed Chassis Lubricated
Manufacturer's Recommended Maintenance Performed
Spark Plugs Replaced
Rear Brake Pads & Rotors Replaced
Automatic Transmission Serviced

90k Miles
Front turnsignal/parking bulb replaced
Oil & Filter changed chassis lubricated

85k Miles
4-wheel alignment Performed
oil and filter changed chassis lubricated
manufacturer's recommended maintenance performed

81k Miles
Vehicle serviced
crankshaft position sensor replaced
engine/powertrain computer/module checked
stabilizer bar links replaced

75k Miles
Passed Emisions

74k Miles
Vehicle Serviced
oil & filter changed chassis lubricated
tire condition and pressure checked
4-wheel alignment performed
front brake pads and rotors replaced
spark plug wires replaced
engine/powertrain computer/module checked

More available if needed.

Thank you guys very much. Greatly appreciated.

 

From the service history it looks like they've been chasing this problem. If you don't have an OBD II reader get one. When the CEL goes on write down the codes and clear. Next time see if the same codes/cylinders show up. I'd go for cleaning or replacing the MAF if the codes jump around to different cylinders. Fuel filter can cause engine stumbling.

That motor takes 8.5 quarts, it's a big sump and won't miss the 1/2 quart though . I hope you specified Mobil 1 or approved synthetic oil and fleece filter. Excess oil fill can cause problems but I don't know about missfires...could be? . If your shop drained the oil from the plug ( with filter loose/removed), put in 8 quarts, and the message returns again then your level sensor is probably off. Looks like it was fairly well maintained.

 

Thanks mleskovar! I'm a huge Mercedes fan, but to be honest, I know nothing about them. I assume I can pick up an ODB II reader from most stores? Is the process of reading/clearing the codes rather simple?

From what I understand... there isn't really anything I can do to diagnose the problem until the CEL turns on again correct?

Thanks

 

Yes, make sure it can clear codes as well as read them. Cheap....$35.

Yes, under the dash on the driver's side next to the steering column is a port that the OBD II reader plugs in to. Flip down a cover and plug it in and read the codes. Follow the OBD II directions for reading and clearing.


Not necessarily, but with the CEL then the codes are somewhat generic. MB can put it on STAR and be more specific in diagnosis, or not.

 

For my penny worth I noticed that the spark plugs were replaced but not the High Tension leads at 96k. The Ht leads do get a little brittle with age they do get stuck to the plugs requiring effort to remove them. If damaged during the spark plug replacement they can cause a misfire. I would suggest that the leads be replaced on cylinders 1 and 6. If this cures the problem then a good suggestion would be to replace the rest too. In total there are 12 HT leads- 2 per cylinder.

Do take care when fitting as the left and right HT leads do have different lengths and have different part numbers.

 

You work for enterprise and bought a rental? Yikes, anyways it doesn't sound too bad probably a bad plug wire or coil none of which are too expensive.

 

It wasn't a rental. It was a personal vehicle that Enterprise Car Sales took in on trade. Just happened to get a great deal on it which is why I purchased it.

I will get an OBD II reader shortly and continue to monitor what happens and pursue the issue from there.

Thank you all very much. I have confidence in this vehicle again now.

 

Typically dieing at idle is symptom of bad crankshaft position sensor and this problem does not set codes or turn on check engine light.

 

Replaced at 74K

 

Replaced at 81k