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Q: Mercedes Benz 1997 E230 stumbling engine

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I own a second-hand Mercedes Benz 1997 E230 WD210.

Occasionally, while driving, the car has had some rough stumbling i.e. choking when accelerating. This happens even at high speed, 80-100kph. Once, it even caused the car to turn off its engine when accelerating out of a traffic light.

I have noticed that the problem seems to arise when the fuel tank is more than 75% full.

In the past 18 months, I have had the fuel pump, fresh air intake and camshaft sensor replaced. It seems that the problem has improved, but not disappeared entirely, causing me some anxiety when driving it over long distances.

What should be the problem?

My car has 18000 miles.
My car has an automatic transmission.

A: The information given states two different ...

The information given states two different vehicles. I will be addressing the first (E230). Its possible with the age of the vehicle that you hare having several issues. You are correct to address sensors, air, and fuel. All of them can cause issues like these.

Lets start with fuel. When you had the fuel pump changed, did you also replace the fuel filter? This should have been done at the same time. The fuel injectors can also be dirty and may need to be cleaned.

If you have not run the vehicle for codes, you will want to do that almost immediately. That way if the computer is picking up on something going wrong, you can start there with your diagnosis.

Oxygen sensors can fail as well causing drivability issues. Again, most of these sensors will trip a code in the computer. However some will not, or some may not be testing bad enough at this point to sound an alarm.

Start with trying to maintain some of the important fuel system components and test everything related to it as you proceed. Start with the simple fixes, and work your way to the more complicated systems. If you would like to have an expert pinpoint the issue in person, a qualified professional from YourMechanic can come to your car’s location to diagnose the hesitation issue so that this gets repaired correctly.

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