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.

 

How many miles are on your MINI? Did your mechanic do a cylinder leak down test?

 

I have own a lawnmower and Dastun that ran great until it was warmed up, in both cases they both lost compression after warm-up. Intake air leak could cause rough idle, you need to get a leakdown test. I have heard of a lot of base MC's having all cylinders between 180-190 after 150k.

 

If the cylinder leak down test comes back good then it could be a timing chain. The vanos units can compensate for a good amount of stretch. And the N12s don't get that rattle when the chain stretches. If the chain stretches too much the intake valve timing goes out just enough to cause the valve to hang open and misfire.

 

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?

 

What did your dealer say on this?

 

I'm still waiting on the mechanic to do a leak down test.

 

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

 

No fuel rail test?

 

No fuel rail test. I think the mechanic was chasing the Mass Air Flow code.

 

78-80% on the leak down test tells me that you have about 20% leak down. So most likely you have valves hanging open. The timing components looking new only tells me that the oil level was kept up and oil changes were done on time. I would check the engine timing and measure the chain. N12 new chain is 62mm. If it stretched more than 5mm then it needs replacement. It could also have a collapsed tensioner for the timing chain which would explain the hot idle issue. When the oil is cold and thick it keeps the tensioner out and when it warms up and thins out the tensioner doesn't keep the chain tight. Also check if the engine is in time I have seen them lose time due to stretch by 1 tooth and cause this.

 

No you need to actually see the fuel rail pressure with the engine running, forget codes as they can only tell you so much. You have no clue what your fuel rail pressure is do you? You need to eliminate this as a possible cause. They haven't done much in the way of helping you, just more questions than answers.

 

They shop is closed now, but I left a message about checking the Fuel Rail pressure and the timing chain again.

To my knowledge the timing chain has never been replaced, but Mini of Pensacola says the tensioner was replaced at 80,000 (I'm currently at 140,000 miles)

Any idea how either of these issues could cause a P115c code?

Thank you all again for the time trouble shooting this a Mini.

 

Just another thought............

The previous owner has had this same issue since last year. The car has essentially been parked for over 8 months due to their frustrations with the car. Any chance the Ethynol or bad gas is causing any of these issues after sitting so long?

I got a really good deal on this car ($2000 US Dollars) that is in almost perfect shape other than the above issues.

 

I agree about forgetting the codes. The rail pressure should be checked but I think that if it was a pressure issue that cylinder 4 would misfire as well since it gets fuel before cylinder 3 or if it was starving for fuel that cylinders 1 and 2 would set misfires since they are after 3 in the rail. If the chain was done at 80k and you have about 140k on it-its coming due to need a replacement soon. N12 chains have no recall or updated parts so that could just be the lifespan of the chain in your engine. The 62mm measurement as new I took myself after the 11th chain I did on a N12 with misfire faults that ended up being the chain. I have not ever found a published spec anywhere. N14 chains start at 64mm and the recall says if its over 68 or 69mm to replace it. That's just 4-5mm stretch.

 

How many tanks of fuel have you driven thru the car? Old gas won't help but you would have more than only 1 cylinder misfiring and most likely some lean O2 codes

 

I just bought the car last week and have driven less than 50 miles. Last week I also got P2187 System too lean at idle bank 1. And also code P2195 Oxygen Sensor Signal Biased / Stuck Lean Bank 1 Sensor 1. However I have not got either code lately.

The mechanic just texted me the following:
One other thing I thought of, when looking at the mass airflow data on the scan tool........."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.

Any thoughts on the air flow here?

 

The reading with the engine off sounds about normal depending on your elevation over sea level. Where I am it usually reads 2.85kgs. The 0 reading concerns me. Have you replaced the mass air at all? Does the car have a standard air filter or a k&n type that uses oil?

 

I have seen the oil type air filters cause mass air problems because they coat the sensor with a film of oil which throws the sensor crazy.

 

And have you ever had any codes relating to the evap system? I've also seen the vent valve under the intake get stuck open and cause lean codes and misfires.

 

The car is totally stock. Standard air filter too.

I am at Sea Level in Florida. Since I have only had the for a week, I do not or have not had any other codes other than described above.

Ed

 

Have you swapped the MAF for another known good one? Have your mechanic read the intake air temp with the key on and engine off when cold and hot. It should read the ambient air temp. if it doesn't -it could be forcing the car rich or lean depending which way it reads.

 

The MAF was replaced 2 years ago by Mini..

I will ask the mechanic to check the temps of the air too

Thanks again
Ed

 

Let me know if you have any success