Hello. I have a 2008 Mini Cooper base, N12 engine. I keep getting the Check Emgine Light with code P0303 Cylinder 3 Misfire. I had it at the shop where the mechanic:
1. Cleaned the Mass Air Flow sensor
2. Replaced Valve Cover gasket
3. Replaced Spark Plugs
4. Changed Serpentine belt
5. Oil and filter change
6. Compression Check. All cylinders were between 150-160.
7. Swapped Coil Packs

He test drove it after completing the work and said the code was reset and the car was running great. I then drove it home and it ran awesome. However, when I pulled into my driveway, the idle was rough again and then the Check Engine Light came back with the Cose P0303!!!!!!!!

I tried the Seafoam through the intake vacuum line and some in the gas tank, but had no luck here.

I called the mechanic and he recommended swapping Fuel Injectors. I reset the Codes and then swapped injector 3 to 4.......but the Check Engine light with P0303 came back!!!!!

It seems to me that when cold, the engine idles great.....but after the engine has warmed up, the idle becomes rough. The car drives great once moving through all 6 gears. Both the mechanic and I are out of ideas. Please help. Any ideas or recommendations are welcome. Thank you.

 

Hi man i feel for you im having the exact same issues with an 07 cooper,have a look at my thread
https://www.northamericanmotoring.co...ml-issues.html

three weeks on and ££££££££££££££ im still having the same problem.....great when cold bag o sh*te when warm...........

All i can think of now is ECU/DME problems im going to get mine tested and reflashed next week............the diaganostic systems on these cars seem useless like you all i was getting was a cylinder misfire......no **** sherlock.....kinda figured that lol......still no closer to solving the problem...let me know how you get on.....

 

My thought.....
Move the fuel injector....
A partially clogged one or failing one can cause issues....
On a gen1 it is simple to do...on a no DI (non-s) gen2 motor it should be similarly easy....then see if the issue follows the moved injector....

 

Oops...just reread...saw you did it...
Fuel psi good on the rail?

 

Just found out tonight when trying to replace the fuel filter its starting to look like some imbecille has installed the wrong fuel pump/sender into my car gonna check tommoro with BMW....madness

 

2007 gen2 cars can be a crazy mix of gen1 and gen2 parts.....just when hanging out at the shop...they have found 2007 gen2 cars with gen1 bits...suspension parts mostly...

 

wow thats crazy man i hate bodgers if your gonna do a job ...do it right man..........i noticed that when i was driving home after buying the car the fuel guage barely moved from full after 100 miles and the rough running started when the guage got to a quarter.........may not be the problem but the housing installed in my car has no fuel filter as it should have....would explain all the idle problems i been having.....

 

For the issues you have man here are the tests i undertook condensed to save you reading my whole post

CHECK OIL LEVEL
CHECK WATER LEVEL
CHECK PLUGS GAP/OILY/BURNT DEPOSITS
CHECK COILS
CHECK INJECTOR WIRING LOOM FOR SPLITS OR EARTHS
CHECK INLET FOR VACCUME LEAKS
CHECK VALVE COVER FOR OIL LEAKS INTO CYL
CHECK FOR OIL ON ANY SPARK PLUGS
CHECK WATER BOTTLE FOR OILY DEPOSITS
CHECK OIL CAP FOR MAYONAISE DEPOSITS
CHECK FUEL FILTER/FUEL PRESSURE

ALSO I CLEANED MY INTAKE WITH SEAFOAM AND CATACLEAN USELESS WASTE OF TIME

DO A COMPRESSION TEST
DO A LEAKDOWN TEST
REPLACE CRANK SENSOR
REPLACE 02 SENSORS

whew lol thats what i did to try and diagnose the problem all to no avail.... it's looking like my issue was the wrong fuel pump,however being Irish i dont expect a quick fix...nothings ever handy lol the only other thing is the DME/ECU seemingly these peugeot engines can and do lose their maps over time.................hope ya get it sorted

 

Thanks for the advice and info. The car is in great shape but it does have 140,000. I got most of the service records from the previous owner, who is a good friend. No record of the timing chain being replaced.

I will call the mechanic and pass the info on to him:
1. Leak down check
2. Fuel rail pressure
3. Timing chain
4. Camshaft Position Sensor

Good info here!

Thanks again

 

Went out this morning to start the car. It started and idles perfectly while cold. Does anyone have any theories or ideas why it only has rough idle when it's warmed up?

 

The ECU/DME compensates when cold delivering more air/ fuel..... also electrical components tend to break down when heat is introduced if they have a fault.

Also if it is an engine problem when cold your oil isnt fully up to temperature and is thicker so that masks any leaking seals and gaskets looks like we both have the same issue i'll let you know how i get on with the fuel pump.

 

Sadly guys fuel pump made zero difference gutted..........still running like crap i'm leaning toward ecu/dme map or a cracked block now...... can't be anything else regardless of the compression test results a crack in the block may not show up on a compression test.... i have noticed i lose a tiny amount of water over a few weeks like maybe 100ml gotta be going somewhere...the oil is clean no mayo on the cap or dipstick,altho the radiator top hose is very firm when hot,also plenty of heat in the car and it has only overheated once in two months due to low water,still the water has to be going somewhere..........

 

Leak down test was competed hot and cold. All 4 cylinders were good at about 78/80. Timing components all look new.
The car started running rough again and now got code P115c and 2B56.

Smoke tested intake no leaks. Cleaned maf. Cleared codes runs smooth again. MAF has been replaced in 2012. Out of ideas.

Please help. Ed

 

Same here Ed i'm at my wits end seems to be running even worse now and im misfiring on two cylinders now use to be just at idle now its the same at all speeds,i have decided to send the ECU/DME off to be tested as i cannot humanly think of anything else seems to be a common problem but no one seems to know what it is lol

 

Thanks for your update. This is maddening

Please let me know how the ECU update goes. Did you pull it out of the car and send it to be updated?

Thanks again
Ed

 

Hi Ed aye i'm gonna remove it myself it's just in the engine bay easy access also spoke to a few guys over on a BMW forum i'm a long time member of they reckon it could be a timing chain slipped a tooth,would explain a lot of our symptoms also i believe the cooper s did indeed suffer from these timing chain issues with castastrophic failures on loads of even low milers,trouble is you need a special timing kit to lock the cam and crank up so it's kinda expensive even to do it yourself,not sure it can be checked without this kit gonna ask my mate tommoro......crazy cars ehhh...

 

I refuse to be beaten by a mere Mini lol.....i WILL get to the bottom of this eventually.....

 

When looking at the mass airflow data on the scan tool with the engine shut off it read: after the engine was running rough, still showing 2.5 kilograms an hour (confused why we would still get a 2.5KG reading with engine shut off). After we did all the work and the engine started running smooth it read 0 kg/h after the engine was shut down.

I just got some more data from the car....hopefully we are narrowing this down.

1. Fuel pressure 53 psi
2. Mass Air Flow 36.5 kilograms an hour at startup. Then 10 kilograms an hour when warm idle with the engine running good.
3. When the engine was running bad, the flow readings continued to read 2.5Kg AFTER the engine was shut off.
4. All air flow temperature readings including ambient are correct.

Any ideas given this data?

Thank you
Ed

 

Sounds like a bad airflow sensor.... The readings would appear to be "stuck", the runs bad....turn it off..the reading stays frozen....know you said you changed it 2 years ago...but stuff does fail....certainly the simplest explanation...
That is purely a guess based on your last post...to have a reading go frozen, car run bad...shutvit off..and have the same reading...might be a simple fix after all.

 

You might try cleaning the air flow sensor

http://www.autozone.com/autozone/acc...entifier=36011

https://www.youtube.com/watch?v=_TO7ZC5N-aA

 

have you looked at the timing on this motor? a bad chain or tensioner and/or vanos unit will cause it to do bad things when warm. it will be running the cam at a different point. i have all of these go bad and with the miles your at, it is very possible. also what kid of gas and octane? a burnt exhaust valve will give you a misfire code also, but I'd lean to timing...

Chad
Detroit Tuned

 

I just picked up a MAF sensor today. I will throw that on the car to see if that improves the situation.
A compression and leak down were completed, so I hope that rules out bad valves.
What symptoms will I get with bad VANOS selenoids?
I may replace timing chain and tensioner just due to the miles. Anyone know the man hours required for this replacement?
The car has been sitting for many months and I'm not sure what gas was put into the car. I just bought it last week. I just bought a new fuel filter, so I intend to drain the tank and replace the fuel filter.

Thanks again
Ed

 

Just carbon built up,dirty intake valves? Needs good cleaning,like walnut shield blast or manual cleaning,Seafoam is not enough...Cold intake temp,rich air/fuel mix ,no CEL and when it warm up,mixture goes too lean...Sometimes "carbon built up" gives strange CEL...

 

I just read this whole thread. I am a 2010 Justa owner. Based on my periodic measuring of timing chain slack, I would expect you are at or above 68 mm of slack where system replacement is needed and could account for your hot running problem. You need a special tool to measure the slack. Also, you did not mention what the plugs looked like, particularly #3. My valve cover gasket still leaks after replacement. Oil could be affecting a coil. Mine leaks a tiny amount of coolant now and then. Former Mini shop foreman admitted they always top these cars up at each service. Good luck with this!

DOC

 

Just an update Ed managed to solve the majority of my problems today,i changed both the camshaft position sensors and the car began running a lot better still misfiring tho,so i rechecked the NEW coilpacks i had installed like three weeks ago turns out one was indeed breaking down i replaced it and the car is running super smooth with the check light gone,feels like a new car....still getting a wee stumble on idle like every three out of five stops at traffic lights like its trying to find a comfortable idle speed between 500rpm and 950rpm i'm convinced this is ecu/dme software issues i'm gonna hook it up to SSS tommoro and have a look otherwise it'll be stealership time for a reflash.........may not apply to you but check all installed parts as in my case the new part was worse than the old lol......