My mini just rolled over 100,000 miles and its starting to show its age unfortunately.

Gas mileage has been getting progressively worse, i'm now down below 30 MPG and there is a decent amount of carbon inside the exhaust that never used to be there. The idle is higher and it seems to surge up and down.

On other cars I've had do this it has always been a vacuum leak of some form causing false air induction so after inspecting all the hoses and gaskets, I decided to tear into it to fix some things.

Valve cover gasket was leaking some, replaced that and spark plug tube seals. I noticed that my crankshaft angle sensor and dipstick tube were leaking, so I took the intake off and replaced the o-rings on those and degreased the front of the engine. I also changed the spark plugs and the coil as preventative maintenance at this point. Throttle body and MAP sensor got a good thorough cleaning at this point too.

Everything back together with all the new parts, a fresh air filter and oil change, and the mileage is worse than ever. Only thing I haven't yet tried is changing out the O2 sensor, which I fully plan on doing soon, but I was wondering if anybody else has experienced this? No codes using the INPA diagnostic tool.

 

I bought an 06 at 100,000 miles, and the mileage was terrible. I changed the spark plugs & wires (both to NGK as described on the board), left the stock coil there though. I replaced the air filter, changed the thermostat (got a water temp warning that led me to that), and when green coolant came out while changing the thermostat, I decided to flush the coolant. While I was changing the thermostat, I took the opportunity to clean the throttle body, since it was right there. Topping it all off, I put fuel injector cleaner in on the next fill-up.


Went from MAYBE 19mpg HWY (avg) if we were lucky, back up to ~30mpg HWY (avg).

 

When the pre-cat O2 sensor went on my Cooper, I dropped from 32-34mpg down to 26mpg. Yes there was a code and MIL. But with 100k on your car, you might want to consider it as maintenance. I believe 100k is the recommended interval for both. I bought an NTK (OE supplier) from Amazon for $108 each. I don't recall the P/N, but there are threads here on the topic if you search. Don't try and cheap out with a Bosch. People report mixed results.

 

Mine has similar problem, and scanned with OBDII scanner, no code, O2 seems fine, any thought?

 

Well, I've been through about three sets of oxygen sensors because I didn't listen to what everybody else had posted here. I replaced them finally with the NTK oxygen sensors about 2 months ago, but I haven't even driven a tank a fuel through it yet so I can't report back on mileage. I was getting consistent oxygen sensor codes with the bosch universal and the bosch direct fit. I can say that the codes have now gone away with two new NTK's but no mileage to report back yet.

 

did you resolve your problem by changing O2?
and did you do a OBD scan? and no code?

 

Theodor - I have '13 non-S & just in the last week have been experiencing similar symptoms. My symptoms are inversely proportionally worse with ambient temperature (so far 20F was coldest). No codes.

So of course I change several things at once!

Added fuel system cleaner, refilled with (hi confidence) good non-eth premium, now weather has warmed back up into the 30's. Problem hasn't returned in last several days.

I doubt that I have solved the problem, so I hooked up my digital volt meter to the accessory power outlet.

What I am seeing is 12V with ignition on, before start. After start, voltage is 11.5V until I rev it past 1500. After the alternator kicks in, it will stay at 14.7V even at idle.

I suspect I have a weak battery but want to replicate the problem with voltmeter data before I change battery (still has orig battery!)

Btw, my car would also miss at idle when I came up to stop light, after driving for several miles at 20F. This is why I am not convinced of root cause yet.

Keep us apprised of your finding; I will do likewise.

 

duplicate deleted

 

In addition to above....don't forget the gas is now " winter fuel" which is %%#%$#%## !!!

Reduces mileage and cars do not like it !!


At least up here in the Northern states.

And make sure you run premium always

 

I apologize to the forum about my above post.

I was trying to respond to this thread on cold idle quality:
Unstable idle at cold start

Don't know how it ended up here.