poor cold starting

[Devonian]

my w210 E200 has started to become very poor at starting on cold mornings. It turns over a lot more that it used to before firing then runs very rough for a few seconds, once warm it is fine. I have replaced the plugs and MAF but still the same. I'm thinking maybe a coil pack at fault? if so how can you tell which one? - or are ther any other suggestions?

 

[robparker]

Try cleaning the throttle body. A duff coil will cause a misfire, possibly even of more note when warm. You can swap the 2 coils around to see if the misfire moves with it, but I dont think a bad coil could cause a poor/slow start from cold

 

[Devonian]

Thanks for the reply, The problem has now got worse in that I can't start it at all today (after not being used foir a few days). I've not had any experience with throttle body before, I assume you are referring to the butterfly valve that is visible when I remove the air filter?. Looking at this (from the air filter end) it is fully open, with the ignition off I can close the butterfly manually, as soon as the ignition is turned on it moves under power to fully open, I assume this is normal?

Any help in method to diagnose the poor starting (or now no starting) would be much appreciated. For a few weeks it has been difficult to start when cold, taking longer to fire then running rough for a few seconds though once warm always started fine. Now it just turns over, sounds like it is firing very occassionaly but not enough to run

 

[Steve@Avantgarde]

Have to go back to basics here, check for fuel pressure first and good spark. My guess is a lack of fuel pressure, possibly caused by a failed regulator inside the fuel filter which would explain its reluctance to start and the rough running...