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%.