My 09fjcw has been have issues with cold start / missfire for about 20 seconds then once it warms up it is fine. Also the car seems to be running rich. The car has 143k miles. It has been at specialty motorwerks in Dayton Ohio for about 2 weeks and they can't seem to figure it out. Hoping someone might shine some light on this.

The car was just carbon cleaned , new plugs , and high pressure fuel pumped tests fine. They said it's only when it's cold.

 

Have you changed your timing chain?

 

no they think it's my coolant sensor

 

Coolant sensor causing rough idle? Say what now. Doubt it.

 

The sensor on the Thermostat is tied into the emissions system, and yes will cause issues like this...

 

Over-engineered. But hey still love these cars.

So the computer is looking for a valid coolant signal/temp and if it doesn't get it...the computer says....f it....I'm just going to run rough?

Great.

 

when cold it reads that engine is hot....at least that is what I have been told. Sorta like not setting the choke before starting older engines I guess.

 

Wouldn't it be nice to have a manual override.

 

would a manic tune over ride this? I just has the thermostat replaced a few months ago. But hey it's mini I have learned anything is possible.

 

Not sure if you are having the same issue, but up until today my mini had been idling VERY roughly. After a few months this escalated into occasional jerks going up steep hills, stalling occassionally (like 3 times in a year) when coming to a stop etc. Plus smelling rich of gasoline. Well finally my CEL came on and was a O2 code. Replaced the UP O2 Sensor and it works beautifully now.