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Discussion Starter #1
Hello to all. This is a long story but I'll try to make a short one.

Here's little specs. My mini is 2014 with automatic transmission. I bought the car 3 years ago. It had 30000 mile on the clock. First thing was getting tuned up with with Celtic Tuning stage 2 programming. This year spring I had quick silver exhaust done (exhaust is from the middle section, no catback). Mini has now 53000 miles on the clock. Otherwise car is totally factory.

Problem started this year about June. And the problem is that everytime I start the mini idle goes suddenly from normal to 500rpm and jumps quickly back to normal. This happens only during startup and it does this sometimes 1-2 times and idle becomes normal after this. It doesn't matter if engine is cold or warm. If I stop and take 5 min brake and come back and startup idle is "crazy" and then goes to normal. If I stop at lights idle is normal. Car performances totally normal, there is no other issues whatsoever. I can drive 200 miles and after turning engine off and then start => idle goes down and quickly jumps back and then settles to normal.

I was taking car to normal service end of July. I mentioned to serviceguy that can you check if there is some simple solution to my idle problem. Guys at service take a look and they found fault codes that cylinder 2 and 3 are missfiring. I asked could they change coils and plugs, but they insisted that they have to open crankcase and check if there is problem with Valvetronic system (what the f.. this has to do with bad idle??). They also said that DME(?) must be updated but I said that it can not be done because it will erase Celtics programming.

Well I took the car off and drove to my friend who programmed car. He told me that change those coils and plugs and come back and we'll check if there is any codes left. I ordered new coils and plugs and changed them this month. I drove back to my friend and there is no more fault codes.. so it fixed that issue but that idle problem is still there. I think those old coils and plugs were original ones from the factory.

Do you happen to know what should I check next?
 

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Discussion Starter #3
have you checked your O2 sensor ?
Nope. Can you explain more? Does O2 sensor has something to do with this? As far as I know, there was no fault codes whatsoever. If O2 sensor is faulty, shouldn't there be some kind of warning message?
 

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mini cooper SD 2015
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if its an intermittent fault the O2 sensor might not show a code, but a bad idle can only be one of three things, fuel spark or oxygen. since you changed your coils and plugs ( spark) next place to look would be oxygen so your O2 sensor or you intake but im sure the intake would be fine but the sensor might be causing you to run slightly lean on a cold start which will make you have a rough idle
 

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Discussion Starter #5 (Edited)
if its an intermittent fault the O2 sensor might not show a code, but a bad idle can only be one of three things, fuel spark or oxygen. since you changed your coils and plugs ( spark) next place to look would be oxygen so your O2 sensor or you intake but im sure the intake would be fine but the sensor might be causing you to run slightly lean on a cold start which will make you have a rough idle
Ok! Nice to know. As far as I know there is two(?) sensors, one before and one after cat. Should I check/change both or just one before cat?

Actually, my wife has this 2009 R56 Cooper with N12 engine and there was this problem that after slowing down to lights or braking in junction idle was almost as low that engine might stall. There was also CEL coming on. Both O2 sensors were bad and after I changed them idle problem was solved. So it makes sense..

Although my car has no problem when driving or slowing down, idle stays where it is supposed to be. Only this startup moment with idle is the problem. But anyway, thanks for thoughts and helping :)

EDIT: yep, two sensors. Both with Bosch labeled ~180€ together..
70318
 

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mini cooper SD 2015
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Ok! Nice to know. As far as I know there is two(?) sensors, one before and one after cat. Should I check/change both or just one before cat?

Actually, my wife has this 2009 R56 Cooper with N12 engine and there was this problem that after slowing down to lights or braking in junction idle was almost as low that engine might stall. There was also CEL coming on. Both O2 sensors were bad and after I changed them idle problem was solved. So it makes sense..

Although my car has no problem when driving or slowing down, idle stays where it is supposed to be. Only this startup moment with idle is the problem. But anyway, thanks for thoughts and helping :)

EDIT: yep, two sensors. Both with Bosch labeled ~180€ together..
View attachment 70318
yeah i would go ahead and change both just to be sure i hope that it solves your issue it sounds like it will keep us updated always happy to help
 

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Discussion Starter #7
yeah i would go ahead and change both just to be sure i hope that it solves your issue it sounds like it will keep us updated always happy to help
Yeah, I will inform if this helps out the problem.

Changing those two seems little a bit harder than my wife's mini :D
Need to perhaps strip down some parts before getting good access?
 

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shouldn't have that much of a problem if you can get the car high up enough, however you may need a special socket or tool when removing or just use a open end spanner.
 

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Discussion Starter #9
shouldn't have that much of a problem if you can get the car high up enough, however you may need a special socket or tool when removing or just use a open end spanner.
Yeah, well that's not a problem, I can lend a lift and I already have that socket tool :)
 

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Are you using a standard air filter (is it clean?) as some oil covered ones (K+N) can contaminate the MAF. To check the MAF is ok unplug it and start the car, if idle is ok plug it back in - if idle is erratic - bad MAF
 

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Discussion Starter #12
Are you using a standard air filter (is it clean?) as some oil covered ones (K+N) can contaminate the MAF. To check the MAF is ok unplug it and start the car, if idle is ok plug it back in - if idle is erratic - bad MAF
This one is easy to test and I will try it.
Actually, I had RAM air airfilter system in car, but I decided to remove it and put original airfilterbox back in to the car. (Reason is, that we have very cold winters, sometimes -30 degrees and it might not work properly)
I could have probably damaged the MAF accidentally when removing and installing, who knows? Thanks for the info :)
 

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Discussion Starter #13
I think MAF sensor is broken. I test it today. Unplugged, start the car cold = no erratic idle or down-up revs. Plugged back = erratic idle. Dang, I think that RAM air filter has broken it (or my assembly). Later evening I was starting the car. Now it got worse. Mini stalled after startup. I started again and after little a bit idle I put it on reverse and it stalled again. Well, got it runnig after little a while and drove to automotive shop to buy CRC MAF cleaning product. Cleaned MAF and let it dry. After plugging it back, started the car (engine was warm) and idle is a little bit better.

MAF sensor was original BOSCH dated 2014-08-11 19:11 so it is factory one. BOSCH part number 0 280 218 266. Checked Autodoc and price is 171,44€ with discount.

Well shiie... that was a one expensive cone filter testing...

I will look forward if cleaning sensor did help it, but I will not count on it.

Live and learn, or how they say it?
 

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At least you now know the problem
Electrical contact cleaner is ok for dust and dirt in the maf but sometimes oil residue wont clean off - worth trying a few times though
 

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Are you using a standard air filter (is it clean?) as some oil covered ones (K+N) can contaminate the MAF. To check the MAF is ok unplug it and start the car, if idle is ok plug it back in - if idle is erratic - bad MAF
Cleaned MAF yesterday and once again today. Coldstarted mini today and seems that erratic idle is gone. I perhaps may saved 170€..

I will drive mini around and inform if bad idle comes back. So far good..

Nice catch, Robby 👍
 

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Discussion Starter #18
Been driving now while and I think MAF is permanently broken. Cleaning doesn't help anymore and idle going down & up happens a lot when engine is warm. And it is only when starting the car, not after. Yesterday it almost stalled again after starting. I think I have to buy new one.. dang, I almost thought I would get away buying it but..
It seems to be on discount at Autodoc. 148€ BOSCH factory original MAF.
 

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Discussion Starter #19
God d***it.. I bought new MAF sensor and installed couple of days ago. Still going sometimes with jumping revs on starting engine. I think I had luck before when unplugging MAF and started cold => no revs going up and down. I was pretty sure new MAF would fix the issue, but no.. back to square one. I hate to throw in partscannon but perhaps next one is to try new oxygen sensors..
I just don't understand that after starting engine and revs going down-up after couple of seconds everything is normal and while driving there is no problems occurring anykind. If someone else could start the engine and I started driving the car I did not know that there was any problem.

I read in some topic, that there is some kind of regulator(?) that might have problems with idling, but mainly with 1.5 litres petrol. I remember that it was kind of vacuum valve or similar that had problems and causing bad idle, but it was causing it all the time..
 

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Before you go in with the parts cannon just have a double check of the wiring. In a previous car I had issues with idle speeds and faults were pointing to the oxygen sensor but it was just that the wires to the sensor had broken. Also anything that is not earthing correctly due to a loose wire can cause intermittent faults.
 
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