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2012 12C Coupe - VR
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My 12C is tuned, and the cold start idle is very rough with RPMs all over the place and feels like the car is shaking for about 60 seconds after starting. Afterwards, it idles smoothly and runs perfectly.

Any idea what is going on? I was told it was the "cam phasers adjusting" and this is normal. Does this make sense?

I read on other blogs that the MAF may need cleaning.
 

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Is it just a super low idle on cold start or when you say "all over the place" the idle is literally jumping around?
 

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Granted my car isn't tuned, but I had a rough idle at cold start and it ended up being the driveline damper. Replaced under warranty.

-Troy
 

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Subscribed. Mine always did exactly what you are describing. I’ve put about 1500 miles on it since I bought it nearly two years ago. I called McLaren Atlanta (where the car came from), and they reassured me that this was normal. Then, a couple of months ago, when I changed the oil, I also removed the intake sound generator, and capped it off with a block-off plate; I’ve only started my car a couple of times since, but I noticed that the engine runs smoothly from the moment it fires up now. Maybe it’s just coincidence, but now that spring is near, I should be using the car some, and I’m anxious to see if that persists.
 

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My 12C is tuned, and the cold start idle is very rough with RPMs all over the place and feels like the car is shaking for about 60 seconds after starting. Afterwards, it idles smoothly and runs perfectly.

Any idea what is going on? I was told it was the "cam phasers adjusting" and this is normal. Does this make sense?

I read on other blogs that the MAF may need cleaning.
Hey Ron -

On all three of my cars (and on both of the 'tuned' ones before and after the tune) I have a rough idle on a cold start and after driving when I come to a stop in front of the garage - unless the A/C is on - then all is well. MNB says: "they all do that when they feel like it".

YMMV of course.

You might consider it an undocumented feature. :D

I pick up the 650S800R today - what are you doing this weekend?
 
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2012 12C Coupe - VR
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Discussion Starter · #6 ·
Hey Ron -

On all three of my cars (and on both of the 'tuned' ones before and after the tune) I have a rough idle on a cold start and after driving when I come to a stop in front of the garage - unless the A/C is on - then all is well. MNB says: "they all do that when they feel like it".

YMMV of course.

You might consider it an undocumented feature. :D

I pick up the 650S800R today - what are you doing this weekend?
Safa at HCD says he can tune the "wah wah wah wah" rough idle out. He says it is the cams moving in position. He figured out a way to improve it with the tune.

It's Easter weekend so of course we have some kid stuff. Would love to check out that 650S-800R soon though!
 

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Sometimes mine runs so rough for a few seconds that the check engine light starts to blink, and then goes away. Again, that phenomenon may be “gone” now, as I mentioned above.
 

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Sometimes mine runs so rough for a few seconds that the check engine light starts to blink, and then goes away. Again, that phenomenon may be “gone” now, as I mentioned above.
Ditto, have that sometimes on my 12C also ! I will be in for regular service soon; I will ask them to run test on cold start and verify if everything ok. Will try to remember to post response, but may be month or so.
 

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Must be normal.
My 12C growls very ugly on cold start.
Then calms down and all is well.
CEL flashing at cold start?

That sounds a lot like cam phasers or Drive Line Damper (DLD) starting to go out.

Invest in an OBDII dongle and cell phone scantool app like DashCmd or Torque to read codes. If the CEL was flashing, you'll have pending codes in there. Best to know what they are, and take pics to supply your service guy. DLD will show as Random Engine Misfire and cam phasers will show as Cam Position Sensor.

Cam phasers and DLD are no joke...if they go completely bad you can trash the motor.

You have an early car? 2012 maybe? Both are noted issues with those.

In general, the cold-start idle roughness (without CEL) is normal and has to do with lighting off the cats for emissions reasons. There is a secondary air injection pump that leans out the mixture a bunch, and the cams are rotated to a position with lots of overlap. This creates tons of heat in the exhaust for maybe 60 seconds to get the cats working quickly. Think of it as a "fire starter log". :)
 

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My car is scheduled for service, hopefully picked up this week, so will put that on list.
Excuse my ignorance, but what are the "cam phasers"; and what exactly is the "drive line damper"? I'll google it, but meanwhile ....
 

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DLD performs the same function that the springs on a typical clutch disc do...damping pulses from the driveline. But since the clutch is buried within the transaxle, that function is instead performed a the juncture between the crankshaft and trans input. It looks like a flywheel with some concentric springs around the perimeter.

Cam phasers are oil-controlled devices that advance/retard the camshaft under control from the ecu. This is done closed loop, so the cam position sensor see where the cam position actually is, and the ecu commands movement towards its goal position based on that. Movement is caused by sending more or less oil pressure via a valve. "Variable Valve Timing" and Vanos are common terms for this.
 

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HI all,

Here is a video of the rough idle of my 12C Spider.
My car is stock so not tuned but I would very much appreciate your advice.


Cold start after 2 days so cold. At 15s mark, one can hear the engine rpm going down and then up and down again.
I am not touching the gas pedal at all. It goes up to 2000rpm by itself and this keeps going even when i go do D mode transmission.
It goes away while driving but if I would go for full stop at within 30 secs of cold start, it would start the same behaviour.
It goes away after 3 mins of driving.
A/C is not activated as you can see during the first 3 secs.
Apologies for the sound hicks during 8 and 10s mark.


This rough idle came up about a year ago. It Surprisingly went away after a major repair to the suspension (Acc replacement) and since this spring it is back. Have driven the car weekly during winter, max 10 days idle.
I did 1 trackday in Spa last week and it seems a bit worse than before the trackday. Always using Total 98 oct Premium Excellium.
Going to the Brussels dealer now Tuesday.
 

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Wow, if you didnt tell us otherwise, that looks like a human hitting the gas to warm up the car! I wonder if it's an automated 'feature' to do that when very cold?

I have heard of others complaining of rough idle, but didn't realize it was like that. From what I recall, others complained to their dealers, and they made some adjustment to minimize/make it go away. But I may be misremembering.
 

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Well it feels like the Engine is nearly stalling and then I assume the ÉCU adds gas so it revs to 2000. Then it falls down again and then back up it goes. A bit like my old 1984 P911 turbo when cold but that is normal with those old injections.
 

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HI all,

Here is a video of the rough idle of my 12C Spider.
My car is stock so not tuned but I would very much appreciate your advice.

https://www.youtube.com/watch?v=u4S6VOqznZ8

Cold start after 2 days so cold. At 15s mark, one can hear the engine rpm going down and then up and down again.
I am not touching the gas pedal at all. It goes up to 2000rpm by itself and this keeps going even when i go do D mode transmission.
It goes away while driving but if I would go for full stop at within 30 secs of cold start, it would start the same behaviour.
It goes away after 3 mins of driving.
A/C is not activated as you can see during the first 3 secs.
Apologies for the sound hicks during 8 and 10s mark.


This rough idle came up about a year ago. It Surprisingly went away after a major repair to the suspension (Acc replacement) and since this spring it is back. Have driven the car weekly during winter, max 10 days idle.
I did 1 trackday in Spa last week and it seems a bit worse than before the trackday. Always using Total 98 oct Premium Excellium.
Going to the Brussels dealer now Tuesday.

Extremely similar to the way mine used to behave frequently on cold start. As I mentioned above, the behavior changed after I deleted my intake sound generator and installed a block-off plate. I’ve cold-started the car now probably 15 times since I did that mod, and it hasn’t done that once. Maybe it’s just a coincidence, but I have to ask- when you had your accumulators replaced, did they also do an annual service where they replaced your intake sound generator (ISG)?
 

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Just chiming in...
I also have a machine gun like sputter for about 10 seconds on cold start up and about 3 times in the last 10 startups had that accompanied with a flashing check engine for about 5-10 secs then the light goes off. Strange.
 

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Just chiming in...
I also have a machine gun like sputter for about 10 seconds on cold start up and about 3 times in the last 10 startups had that accompanied with a flashing check engine for about 5-10 secs then the light goes off. Strange.
Check coil pack.

-Troy
 

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DLD performs the same function that the springs on a typical clutch disc do...damping pulses from the driveline. But since the clutch is buried within the transaxle, that function is instead performed a the juncture between the crankshaft and trans input. It looks like a flywheel with some concentric springs around the perimeter.

Cam phasers are oil-controlled devices that advance/retard the camshaft under control from the ecu. This is done closed loop, so the cam position sensor see where the cam position actually is, and the ecu commands movement towards its goal position based on that. Movement is caused by sending more or less oil pressure via a valve. "Variable Valve Timing" and Vanos are common terms for this.

@AWH has expertly diagnosed these two different issues quite well.


Cam Phasers - Expect stored "Cam Position Codes" if this is your real issue

DriveLine Damper - Expect stored "Multiple Misfire Codes" on cylinders 5,6,7 & 8 (Bank 2 only)


I had the Driveline Damper issue. The first step I took was a natural one. I replaced all 8 spark plugs and coil packs. This still did not resolve the rough cold starts or the random misfire codes. I then thought maybe it was just an electrical gremlin?

Then as I researched more I started to imagine my multiple misfires and random flashing check engine lights could only be due to something like a Cam position or other Timing issue.

Not knowing about the ‘odd vibrations & harmonics’ created by the mechanical Driveline Damper being worn or broken can easily take you down the wrong diagnostic path toward Cam Phaser replacement. This is what I thought was going to be my problem.

In reality the sensitive electronics on the M383T engine interprets the odd vibrations & harmonics resulting from a defective Driveline Damper as a different issue and the ECU instead interprets this information as random misfires on any/all of the Left Hand Bank of cylinders (the driver side in the USA) .

I have spoken with more than one experienced McLaren Technician and described the random 45 second rough idle on startup, random flashing check engine light when car is apparently running smoothly combined with P0300 Random Misfire codes only on Bank 2 cylinders 5,6,7 or 8. Every time the Technician has immediately said the “DRIVELINE DAMPER” is bad, inspect it then replace it. so again @AWH has nailed it.

FWI – GOOD NEWS - The Driveline Damper can be visually inspected in the vehicle by removing the Starter and carefully inspecting the damper springs for damage using a bore-scope camera.

#16 in the image below is the Driveline Damper which is hidden/fully enclosed between the engine and the transmission housing. (Not to be confused with the Crank Shaft Damper #19 that is visibly exposed on the front of the engine)
200391
 

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And here is a link to anther thread showing an actual picture of the broken Driveline Damper springs

 
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