Turning the key to "on" for a few seconds will activate the fuel pump in the fuel tank before starting the engine. You will hear a slight buzz in the rear of the car. This will fully pressurize the fuel line, making fuel more instantly available at the injectors.

 

Ethanol is almost 3.5x more viscous than MtBE (at 68 F). I wonder if, without the fuel line fully pressurized and at colder temps, the Ethanol is restricting fuel flow just barely enough to cause the engine to run rough.

Anyone experiencing this issue able to test and see if the engine isn't getting enough fuel?

I'm really going for a shot in the dark here but if this is the problem then perhaps a slightly stronger fuel pump would resolve the issue. Or, possibly even modifying the existing one to give it a little more voltage would kick it up enough.

But, what do I know? One semester of college chemistry (the only chemistry I've ever had in my entire life) and not a day of any legitimate engineering coursework, and I think I can solve this issue over the internet?It's okay, I stayed at a Holiday Inn Express last night.

 

Since the fall I have had difficulty starting my 2002 C230K in the morning and after work. I have to hold the key for a few seconds before the engine "catches". Never had to do this before. Once it is started though, it runs smooth. MPGs haven't changed much. No error messages.

I've cleaned the MAF, replaced the spark plugs (with OEM NGKs), and put injector cleaner in two tank fulls. The battery is new.

I have 90,000 miles. I thought about replacing the MAF but I'm not sure the ECO reads the MAF on startup anyway so it probably won't make a difference. Anyone know?

 

I always use 93 and have this problem in the morning too. It has been happening more often now that is it below 30 here.

 

I'm located in Seattle, WA and noticed the same issue with my first start. If I understand correctly, the ECO doesn't 'look' for the MAF at start. ECO uses a default cold-start map to fuel our cars... unfortunately, the M271's seem to be notoriously lean in their mapping. Not a good deal with anything over single-digit percentages of ethanol. That said, ithere's no damage being done... it's just irritating.