Hey guys and gals,
My name is Tyler and I own a 2007 r56 MCS with 125000 miles. I live in maryland and we recently got into the cold months and my car has been mean to me. Upon starting in the morning my car sometimes stalls completely after idling for 5 secs, sometimes it doesn't. But most times the car will stutter and bogg VERY badly when I first give it has after letting it warm up. I've read that it could be a possible HPFP issue (big $$$), a carbon buildup issue, or maybe a fuel filter issue? ? I have no idea what it could be, but it was running perfectly until it got below 40 degrees here. The weirdest part is that I'm not getting any CELs.....which gives me no codes and nothing to go by. So I'm asking the gurus here to please help me out in trying to diagnose this issue.

thanks,
Tyler

 

Also wanted to add that the car runs fine once I've been driving for like 3 mins. I've also put some BGK44 into the fuel tank, thought it worked for a few days, but tonight as I was leaving work the problem came again with full force.

 

Hey Shady,

I had these symptoms with my MCS and read a ton of threads on the subject. I went through a huge troubleshooting session with this on my '07 MCS, let me see if I can possibly save you a headache. I eventually started getting check engine lights, but read on.

Things I tried:
-Coils
-Plugs
-Both O2 sensors
-HPFP
-Fuel Filter
-Carbon Cleaning (though it did need it, you should consider this a preventive maintenance item). I DIY'd this.
-Coolant temperature sensor (was bad/leaking which is a HUGE problem, read on)
-Thermostat

What it ended up being...
-ECU
-Engine Wiring Harness

Why?

Because when the coolant temp sensor goes bad on these cars, the sensor leaks coolant back into the weather tight harness connector and allows the coolant system's pressure into the wiring harness.

It basically turns your engine harness into coolant plumbing. Mine was so bad that it had fed coolant through the wiring harness back to the ECU and filled one of the main connectors with coolant. I of course had no idea this had happened and it must have been like this for some time since the coolant had rotted off 3 pins of the ECU, which were the ones responsible for O2 and MAP sensor.

Do yourself a favor and before replacing anything, pull the connector off of the coolant temp sensor and see if there's any leakage, and also unplug your ECU connectors to see if it is contaminated from a previous owner's mishap. Perhaps investigate the back of the coolant temp connector to see if there has been any seepage.

Hope that helps. It's expensive, but it's also expensive to replace a bunch of stuff you don't need to replace.

Just started my MCS yesterday in -20 conditions and it fired right up no issue, and it used to be a huge PITA. So much so that we bought my wife a new car and I inherited the MCS!

 

thanks for the reply! This is all extremely useful information, almost like a check list. I appreciate it. I'll pull the coolant temp sensor and check out the ecu today and let you know what I find.

thanks!!!!
tyler

 

I had a similar issue it ended up being the HPFP
Mini cover these under warranty. You have a 2007 like I do so the warranty expires in 2017!!
Make an appointment soon before you miss out on a free HPFP including labor

 

isn't it only covered up to 10 years or 120000 miles? I'm at 125000 miles. I emailed them two days ago without a response, so we will see.

thanks
tyler
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