7

It's me again. 2008 MINI Cooper S w/ dealer-installed JCW package (chip tune, larger air intake, larger cat-back exhaust). I thought everything was fine after resetting my ECU last week, but had bad misfiring at idle again this morning which set the random misfire code. Since it's happening across all cylinders, I'm a bit stumped.

Here's what I've done:

  • Replaced spark plugs
  • Replaced cracked air intake
  • Cleaned MAF sensor
  • Reset ECU

The engine has the coils on the plugs, so no chance of a bad coil or bad wires.

I've also purchased a USB scan tool with some software, so I can retrieve any diagnostic info the ECU is putting out. My long-term fuel trim (as of last week) is slightly negative (-2.5%), short-term is right at 0%, fluctuating up and down as the engine speed increases and decreases. This is after a week of daily driving, mix of highway and city conditions.

The misfiring only happens in open loop mode. Once the car has warmed up and switched over, it runs perfectly. It seems that it's running too rich, as I get a fair bit of gray smoke out of the exhaust as it's stumbling.

Failing O2 sensors? Failing idle-control valve? Time to give up and take it to the shop? What should I look for in my scanning software?

(previous question: Lack of power when cold under load)

edit: plugged in the scan tool when I got home. Random misfire plus misfire in 2 and 4. LTFT is back up to 0%.

Spivonious
  • 982
  • 2
  • 10
  • 25

4 Answers4

5

It was the high pressure fuel pump. After letting it sit overnight, the dealership was able to reproduce the issue and replaced the pump under the extended warranty. The car is driving like it did when I bought it two years ago. No more trouble starting, no more stumbling when accelerating when cold.

Thanks to everyone for your suggestions!

Spivonious
  • 982
  • 2
  • 10
  • 25
1

2011 R57 S cabrio. I had identical issue. Misfires all cylinders. Replaced HPFP, coils, walnut blast. ALL FAILED. Engine limp mode returns. Finally checked fuel filter (75k miles). Very dirty. Replaced. Runs like new. $30 for kit. 30 minutes DIY.

R57 S Cabrio
  • 11
  • 1
0

Clean the IACV. Sometimes it does the trick. Which grade and type of fuel does it run on? After cleaning the IACV, check the TPS, reset/restart the ECU try reprogramming the idle after that.

Lawyer Aidroos
  • 696
  • 5
  • 15
0

Had the same problem. After compression check found no4 cylinder had low compression at around 165. Thought the worse but the pressure was holding so no leak down. Turned out to be an easy fix. Removed the rocker cover and inspected the valve springs for breakages none found. Removed the exhaust tappit rail. This can be done without removing the camshaft 5 simple bolts. Removed the tappits for no4 cylinder and on inspection found some wear and pitting on the roller. Replaced the tappit erased the fault code all now solved a cheap and easy fix. Ps the traction control light also was also coming on that too is now fixed. I hope this helps someone it only takes around 45 mins to achieve.

Marko
  • 1