As long as I've owned my '11 MCS, it's idled poorly when cold starting in cold weather. Now that I'm living somewhere that actually gets cold regularly, it has started to become somewhat annoying. The engine idle "hunts" for a little while before stabilizing at the normal RPM. I got a check engine light which turned out to be cylinder 1 misfire detected, but it's only occurred once in dozens of cold starts. There are no issues with driveability. I'm at about 50k miles. My thought is that it's possibly carbon buildup on the intake valves.

 

You didn't say how many miles? I could be wrong, but I think a '11 has the n18 engine, only a few reports on carbon build up on that engine. Usually if it is carbon build up, you would see driveability issues..

 

I'm around 50,000. I actually got the same cylinder 1 misfire again this morning. Maybe something with the ignition system or injector? It seems odd that is only occurs on a cold start after sitting for a day or more. You'd think that the issue would show itself under heavy load as well.

 

I would check the plug and the coil in cylinder ones, maybe moisture ? Also check the harness is clipped all the way to the coil. If its the throttle jumping around , how cold is it where you are ?

 

I will check to make sure the harness is secure and pull the plugs and compare them this weekend. Should checking the coil be done by swapping it to a different cylinder and checking if the misfire remains or moves to the new cylinder? It's about 45 degrees F, so not even that cold.

 

Have you done a carbon cleaning? I had the same issue at about 75,000 miles, and had the valves cleaned. Problem solved 18 months later I'm at 106,000 and it's happening again. Going to have Helix do my clutch/flywheel and carbon cleaning while I'm there.

 

I have the issue where I'll cold start, and for the first 5 minutes or so the engine will idle around 700 RPM, dip to 300-400 RPM, chug a bit, and jump back up to normal idle... My Pepper has 42,000 miles on her. This doesn't always happen. I'd say it happens about 40% of the time.

 

No carbon cleaning yet. What year is your car?

 

2007. If you haven't done it, I'd suggest it, regardless of the year of your car.

 

You could do the carbon cleaning. You will be surprised how dirty the intake valves can get. I would check all the electrical first. Coil and plugs such. Then carbon clean.


Carbon cleaning DIY:

https://www.northamericanmotoring.co...-cleaning.html

 

I'm trying to understand how those parts work. I imagine that you pull the intake manifold and the elbow piece inserts into the intake area of the head while the tubing connects to the media blaster and inserts through the hole in the elbow. Do you move the tubing around while blasting to reach the build up and periodically remove the whole setup to check for progress? It doesn't actually look that difficult, but seeing your work seems like a problem.

 

My car does this exact same thing and I only have 9K miles on it. once it gets to about 80C the problem disappears. I've had one pending CEL that read cylinder 3 misfire but then went away after a few more cycles.

All i have to do is blip the throttle when cold at idle and I can reproduce this problem until it gets up to temp. I don't see this as a carbon build up issue. I've swapped injector, plug, and coil all to no avail. Anyone ever isolate this?

Specs:
2013 Cooper S Hardtop, N18 engine, 9,XXX miles, 100% stock.

 

did you ever fix this issue?

 

is this on an n18 motor? If so did you ever find out what the issue was?

 

Believe it or not, I still have my mini. It has 32,XXX and no longer exhibits this issue. Don’t remember when it stopped, unfortunately. Over the years I’ve made some mods that may have improved idle due to better breathability, but couldn’t correlate anything definitively to fixing the issue. Here are the mods:

1. Swapped cat back exhaust for factory JCW LCI of same era exhaust (cut and clamp like you would with the jwc kit retrofit designed for MCS of this era)
2. Replaced the baffled hot side boost tube with way motor works straight pipe (https://www.waymotorworks.com/wmw-re...7-r58-r59.html)
3. Replaced paper air filter with K&N high flow filter
4. Installed a BMS JB+ piggyback tune module at the MAF at the 80% setting

Hope that helps!

 

Hey, I have got exact same issue. it started 1 year ago after i ran out of fuel.
I have some mods like, borla exhaust, scorpion downpipe, NM Piping, Nm intake, Wagner Intercooler.

I Replaced MAF, thermostat, Upper O2 sensor, Spark Plugs, Coils, HPFP all of this parts for ZERO result.

checked for compression on cold and on warm engine - 13-14 Bar among all 4 cylinders.

checked for boost/vac Leak - nothing.

removed and cleaned Vanos solenoids.

But Still got nothing. I'm going to replace injectors soon. Do you think this will help "?

P.s. My intake valves are pretty clean.

 

Hey, I have got exact same issue. it started 1 year ago after i ran out of fuel.
I have some mods like, borla exhaust, scorpion downpipe, NM Piping, Nm intake, Wagner Intercooler.

I Replaced MAF, thermostat, Upper O2 sensor, Spark Plugs, Coils, HPFP all of this parts for ZERO result.

checked for compression on cold and on warm engine - 13-14 Bar among all 4 cylinders.

checked for boost/vac Leak - nothing.

removed and cleaned Vanos solenoids.

But Still got nothing. I'm going to replace injectors soon. Do you think this will help "?

P.s. My intake valves are pretty clean.

 

Hey, I have the same issue with 2011 MCS N18, misfires on cylinder 2 when cold just on the first start of the day. Changed sparkplugs and coils still the same. Did any of you figure out what it was?
Diagnostics are showing single digit misfires on all cylinders but over 300 on cylinder 2 on cold start, later starts of the day are not having any any misfires.

 

With misfires at all cylinders the cause is common to all cylinders.

I note the misfires are after cold start. Later in the day -- with the engine probably still warm -- no misfires. This suggests an intake air leak a rather small one that causes the cold engine to run a bit too lean.

But...

I had a car that would misfire after a cold start. As was my habit I'd let the cold engine idle just long enough for the high cold idle speed to drop which was a sign the engine controller was switching from open loop mode to closed loop mode.

But every time I waited for the idle speed to drop misfires -- I could barely feel the engine shake a bit -- and the CEL would come on. Engine never misfired any other time. Talked to a tech. He said could be oen or more lazy injectors. But the cost to replace these was rather high. Tech suggested I wait and if the misfires got worse then new injector time.

I took to almost immediately after cold start rather than waiting I'd gently back the car out of the carport and mosey on down to the street and then drive to work. No misfires. So I did this to the point it became a habit and I pretty much forgot about the misfires.

At 132K miles the O2 sensors were replaced. One had gone bad its heater died. Engine felt ok but emission testing required the CEL be dark and there were no pending codes. So I had all 4 sensors replaced. After the engine ran better. I didn't expect this.

Didn't realize it but at some point I had reverted to my habit of letting the engine idle a bit after a cold start. Then it dawned on me no more CEL no more misfires. Now I'm not recommending you rush out and replace all O2 sensors.

What you can try if you want is get a bottle of Techron and use according to directions. It has been my experience when after using Shell V-Power for some months on a very regular basis when I switched to Chevron Supreme (with Techron) one of my cars the engine perked up after not even going through a full tank of fuel. However, another car which had also been regularly fueled with Shell V-Power when switched to Chevron Supreme didn't react one way or the other.

I have never experienced misfires from this but I have with a couple of my cars experienced some rather "strange" behavior: The radio/NAV system not working right, and specifically an "app" that displays graphically on the LCD engine telemetry (coolant temp, oil temp, oil pressure, and battery voltage) would fail to load. A few times upon boot up the radio/NAV LCD displayed wide vertical blue bars. Another car this app would load but it could load right away or take minutes to load. And one car believe it or not the +paddle shifter when used instead of an upshift would *downshift* the transmission. Long story short (better late than never...) for the paddle behavior an ECU/TCU flash played a major role in addressing this behavior. But the other behavior what proved to fix it was just driving the car more. These two cars didn't like to sit unused. While the engine would start ok albeit with a tiny barely noticeable slower crank the other odd behavior was there. With more and regular driving all odd behavior was gone.

I mention this just to make you aware that a car not used often enough can manifest untoward behavior that one might at first not suspect. I note the misfires are present at cold start presumably after the far has sat unused for a while. Later in the day the misfires don't happen. Could be temperature related sure. But could be the start later in the day is better because of the run time the engine received earlier which allowed the battery to be topped up.