Diagnosing RPM Idle Issues in a MINI Cooper

mini_cooper_idle

Back in 2012 I bought a 2009 MINI Cooper hatchback to replace the aging 2004 BMW 330i ZHP that was rapidly approaching the point where a bunch of expensive work would be needed on a regular basis. Bimmer was a wonderful performance car but at 130K miles it was definitely a liability. I wanted to replace it with something sporty yet “frugal” and after multiple test drives of different makes and models I decided on an R56 MINI Cooper with a naturally aspirated non-turbo N12 engine and a 6-speed manual transmission. If you search for “MINI Cooper problems” you will find enough to run the other way. However, if you do a bit of digging you’ll find that most issues discussed ad nauseam on various forums are mostly for a Cooper S i.e. turbo engine. Since I wanted something reasonably reliable and easy to DIY, I decided to go with a base model known as “Justa” as in “Just a Cooper”. After 4 years of ownership the car proved to be as reliable as a Toyota Corolla…until now.

Of course, most newer cars will run great for the first 50-60 thousand miles anyway. I bought the MINI Cooper with 20,000 miles on the odometer and added over 30,000 trouble-free miles. Well, not quite I guess. I just took a peek at the maintenance log and do see 2 issues that fall into a “problem” category: rear sway bar end links and a water pump replacement – both at around 40,000 miles. That’s not something I’d expect to replace given such a low mileage. A dealer would charge about $1,000 in parts and labor, which is a steep price to pay for the “privilege” of having a sporty British/German car. Luckily I had all the tools necessary to DIY both projects so it cost me just $60 in parts plus my own labor. Cheap and a good learning experience, especially replacing the water pump which required dropping the engine :\

Other than these two things the Cooper ran top notch until 2 weeks ago when it didn’t. When I started the car one morning the RPMs were all over the place instead of staying high for a minute and then dropping below 1,000 after warm up as usual. Now the RPMs were bouncing between 500 and 1,900. The engine seemed like it was going to stall.

There was no Check Engine Light (CEL) on the dashboard. I drove it to work and it was perfectly fine on a highway but anytime I came to a stop the RPMs would start jumping around and the car actually stalled a few times. There was obviously an issue with the idle.

Here is a video showing bouncing surging RPMs after driving 30 minutes on a highway. My foot is off the gas the entire time:

It’s difficult to troubleshoot issues like this without a CEL. I started by checking the easy things first. Gas cap securely on? Engine air filter clean? Oil dipstick firmly in place and not loose? Engine oil level OK? Everything checked out.

For any idling issues it’s a good idea to check for vacuum leaks. I bought a can of carb cleaner and sprayed around the intake manifold to see for any change in engine speed, which is a tried and true method for quickly finding leaks. Nothing suspicious there.

Next I took off the intake boot that connects the air-box with the throttle body. The rubber can crack over time and create a leak that will mess with the idle. Previous test with a carb cleaner should usually catch any intake boot problems but it’s easy to take it off and visually inspect as well.

This gave me a chance to clean the mass airflow sensor (MAF) which is inside the intake boot. I used a can of electric contact cleaner to spray the sensor to remove any dirt that may be affecting it’s ability to provide valid readings to the ECU that controls the idle.   

The erratic RPM issue still continued. I didn’t want to start throwing expensive parts at the engine hoping that one of them will fix the problem. That’s a common approach in a situation like this but not a cheap one. The car was driveable so I decided to wait and see if the CEL will come on.

A couple of days later when the Mini was experiencing a particularly violent shudder at idle, the engine stalled out and the CEL finally went on. I don’t usually cheer for Check Engine Lights but seeing it light up on the dashboard made my day!

I pulled these codes with my trusty engine error code reader:

  • P0015 – “B” Camshaft Position -Timing Over-Retarded (Bank 1)
  • P2187 – system too lean at idle bank 1
  • P0300 – multiple cylinder misfire
  • P0301 – misfire at cylinder 1
  • P0302 – misfire at cylinder 2
  • P0303 – misfire at cylinder 3
  • P0304 – misfire at cylinder 4   

Looks scary but at least now I had something to work with.

Lots of different things can cause any of these error codes but again, a sensible approach is to try some easier stuff first before moving on to parts replacement.

There are dozens of sensors supplying critical information to the ECU at all times. Pretty much everything is electronically controlled on today’s engines and it’s only a matter of time before they start failing. Fragile plastic electronic sensors attached to a lump of extremely hot aluminum never made sense to me, but I’m definitely not an auto engineer! I do know for a fact that sensors can and do fail even at 50,000 miles – especially on European cars. I’ve replaced a fair share of them myself on my previous 3 BMWs.

First I tested the intake and exhaust camshaft sensors using my multimeter. It is very easy to do if you follow these exceptional instructions from Pelican Parts. Both sensors seemed to respond and work as expected.

Next I wanted to see if cleaning and swapping the two VANOS solenoids (on the intake and the exhaust camshafts) would lead to any changes in idle performance and/or error code changing from camshaft “B” to camshaft “A”. If it did, it would be a good indication that one of the sensors is bad, usually the one that the error would follow.

This is a little more involved than the camshaft sensor test but still relatively easy if you follow another great set of instructions from Pelican Parts. After cleaning the solenoids with brake cleaner, blowing off with compressed air, swapping locations, reinstalling and clearing the error codes the idling problem did seem to become a bit less apparent but it could be the placebo effect talking. The codes came back after a day of driving as well.

Of course there was still a chance that one or both VANOS solenoids were bad but they are not cheap so I wanted to try a couple of other things still.

At over 50,000 miles my car was pretty close to needing a new set of spark plugs. Of course if you go by what Mini recommends I still had a long way to go since they recommend a 100,000 mile interval between spark plug changes… which is insane. Personally I’ve never ran a sat of plugs for more than 60,000 miles. Spark plugs are cheap and a DIY change on a Mini Cooper is a 30-minute job tops. You’ll need a cold engine, a T-30 Torx bit, a socket wrench with an extension, a torque wrench, a special 12-point spark plug socket and some anti-seize. Also they don’t mention it in the instructions but the correct torque for the R56 Mini Cooper (MK2) is 17 ft/lbs.  

And of course you’ll need a set of 4 spark plugs. I decided to try Denso SXU22HCR11S Iridium Long Life Spark Plugs instead of the Beru brand that Mini chose for these cars. I read good reviews plus Densos are cheaper so I figured I’d give it a shot. Another thing I like about Densos is that, unlike Berus, they work with a regular 6-point spark plug socket you can find anywhere. The less specialty tools I need to work on my car the better I feel about my chances of repairing the car away from my nicely equipped garage.

After the new spark plugs were in I cleared the codes and started the car. I immediately noticed a much smoother idle! A test drive confirmed that the car was doing much better now. There was still some small variations in idle RPMs but nothing like what you saw in the video above. After driving a couple of days the codes did not come back either.

Things were definitely moving in the right direction but there was still room for improvement. After thinking about the next steps I remembered that there were several times that I used mid-grade gas instead of the recommended 91+ premium. While the car’s computer will adjust to a lower-grade gas, it’s definitely something that could potentially lead to some issues down the road.

I figured that now would be a perfect time to try adding some fuel system cleaner to see if it helps with the remaining idling issues. I’ve regularly used Techron fuel system cleaner in the past but for some reason I haven’t done it even once on the Mini. It’s cheap and it does work, at least based on my previous experience with higher mileage cars.

There is nothing to it: the next time you fill up add a bottle of Techron cleaner to your tank before you pump the gas. Techron will mix with the gas and it will clean out the fuel system as the fuel pump brings the gas and the cleaner to where it needs to go.

After one bottle of Techron I noticed that the bouncing RPM problem was completely resolved! The slight variation in idling left over after a spark plug change was gone and the car was back to 100%. I decided to run another bottle of Techron through to make sure everything was sparkly clean. Going forward, I will run a bottle at every oil change.

I’m still not 100% sure what caused the issue in the first place: bad fuel, dirty injectors, dirty solenoids (they didn’t look dirty though) or bad spark plugs. It could be that bad fuel caused other issues, like spark plugs going bad or something else. Whatever it was, I’m very glad that the problem seems to be resolved.

Issues like these can bankrupt you if you go to a dealer. There is no clear indication of what is wrong and the dealer might spend many expensive hours on diagnostics without finding out what’s wrong. Their default approach in this situation is to start changing parts and saying “well we tried this but it seems you now need this…” They are spending your money so there is no incentive to minimize expenses. Actually, it’s quite the opposite. Don’t believe me? Take a look at these comments on a YouTube video posted by another MINI Cooper owner with a similar idle surging problem. This sounds like a major pain and he actually lucked out in terms of $$ – it could’ve been much worse if not for his persistence!

mini_cooper_idle_1

You can do everything described in this post and it won’t take any more time than the endless trips to a dealership. Total cost was under $60 for the spark plugs and the 2 bottles of Techron. I shudder to think what this issue would cost to troubleshoot at a dealer…    

2 thoughts on “Diagnosing RPM Idle Issues in a MINI Cooper

  1. Amazing post! Even though I don’t own a mini, I was hooked 🙂

    Would you recommend using the same Techron on a w203? Didn’t see any problems but it takes things to the better, then why not?

    • The answer is ABSOLUTELY!

      My wife drives a 2003 Mercedes-Benz C320 (w203) and I add a bottle of Techron at each oil change. The car has 135,000 miles on it and the engine runs great. I would say that ANY car with 40,000+ miles should get on a Techron program if you want to minimize a chance of any engine issues. It really does work wonders. Actually, I just ordered a case of 6 Techron bottles which makes it $6 per bottle that I can add at each oil change on the MINI and the Benz.

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