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Discussion Starter · #1 ·
The ol' MKV had a rough time starting this morning and then the blinking CEL came on with a rough idle. This went away after about 15 seconds and it drove fine. I'm thinking I should maybe replace the plugs and coil packs. I think it was done 40k miles ago @ 100k but I'm not sure.

Should I bother? It was pretty cold out this morning but I don't see that causing a misfire...

I noticed some very neon-green looking fluid underneath my car in the snow yesterday too, no smell to it (thought it was gas at first). Not sure why I included that here but what the hell.

Thanks!
 

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Cold start misfires are usually because of a bad maf. Went through that first hand with my passat. Easy test, just unplug the sensor on a cold start and see what happens.
 

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Discussion Starter · #4 ·
Cold start misfires are usually because of a bad maf. Went through that first hand with my passat. Easy test, just unplug the sensor on a cold start and see what happens.
What would I be looking for? If the mass airflow sensor is unplugged, the engine with buck right? I don't follow
 

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What would I be looking for? If the mass airflow sensor is unplugged, the engine with buck right? I don't follow
Unplugging the sensor will force the car to a preset fuel trim for the car. But the goal in unplugging it is to diagnose the cold start misfires. So if you unplug it, and it has to be on the first start up of the day. Anyways, when you start the car, if the light doesn't flash and the car isn't misfiring, the sensor is at fault.

If does still misfire, the sensor is not your issue.
 

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Discussion Starter · #6 ·
Unplugging the sensor will force the car to a preset fuel trim for the car. But the goal in unplugging it is to diagnose the cold start misfires. So if you unplug it, and it has to be on the first start up of the day. Anyways, when you start the car, if the light doesn't flash and the car isn't misfiring, the sensor is at fault.

If does still misfire, the sensor is not your issue.
So I'd only want to do this if the engine feels like its misfiring at startup right? If I turn it on and its running fine, pulling the sensor out wouldn't tell me anything would it?
 

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So I'd only want to do this if the engine feels like its misfiring at startup right? If I turn it on and its running fine, pulling the sensor out wouldn't tell me anything would it?
Just unplug the electrical connector prior to starting the car. If the misfires stop there is your answer. You can repeat this over a few days if you want to be certain.
 
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