So my 09 MCSa has been basically problem-free since mile 1, but yesterday (now at 27k) I began to notice an odd problem. When taking off from a stop in 1st or 2nd gear (I'm in manual mode 99% of the time, btw) the car is erratic and jerky in acceleration up until about 3k rpm. It acts like I'm fluttering the gas pedal, but I'm merely applying steady pressure. I can feel the car hesitating and dropping in power for a split second several times in succession in pretty much every gear when I'm at part-throttle. It exhibits the same random hesitation even when I mash the gas, although after getting above 3k rpm or so it seems to run fine.

I have the DDM Street intake on the car, so I can hear the turbo and bypass valve pretty clearly when this is happening. When I roll into the throttle a little bit, it sounds like the car is quickly and repeatedly letting off the throttle and reapplying it, although from staring at the tach I notice no drop in RPM when this occurs. I figured maybe it was just a bad tank of gas, but it didn't start having this weird problem until I had already went around 120 miles on this tank.

I'm also starting to wonder if it's not the HPFP, since I've had another very sporadic issue for quite awhile now as well but I've pretty much ignored it since it didn't seem like a big deal. For the last 2 winters, the car has randomly hesitated and sputtered at idle while in gear when the motor is cold. Rarely in the mornings, when I put the car in reverse to get out of my driveway, it will sputter and the rpm's will fluctuate for a couple seconds, and then return to normal. Other times, when I'm leaving work and the car has sat for 8 hours, it will hesitate in almost the same manner. During those times, I'll put it in gear, drive down the entrance road to my office (which is about a half a mile), and when I come to a stop before hitting the main road, it will THEN do this odd hesitation and rpm stutter for a few seconds. If I get on the throttle or just sit there until the idle stabilizes, things will act completely normal for the rest of the trip.

Anyone have any thoughts? Vacuum leak somewhere maybe? Not really sure where all the hoses are on this thing, but from a quick look under the hood, everything seemed normal. I guess first of all I'll just slowly burn through this tank of gas and pick up some injector cleaner as well as get gas elsewhere and see how that goes.

While reading your post, my first thoughts were two of the usual suspects:

• Carbon build-up
• HPFP

Another remote possibility is you've gotten some moisture (water) in your fuel tank.

Could very well be.. As an update, while out driving on the highway the car again stuttered a bit, but this time it threw 2 codes: P115D and P129D. Maybe I need to clean the MAF, I think P115D has to do with that. P129D I have no idea..

Yeah, P115D seems associated with the MAF; there's something the car doesn't like there...

Can't seem to find anything listed for P129D, though...?

Welp, cleaning the MAF off with cleaning spray didn't help, definitely still there. The odd thing is that it normally only acts weird at low rpm, moderate/high load.. Although it only threw the codes on the highway.

* MINI DTC P115D (0x2774, 0x2B55, 0x2B57, or 0x2B5B) - Mass Air Volume (MAF) Flow 'A' Too Hgh
* MINI DTC P129D (0x2B73) - Manifold Absolute Pressure (MAP) Maximum Pressure Implausible

Any modifications to the vehicle currently?
Do you have an atmospheric-dump BOV installed?

The ECU is seeing two things going on: first, is the MAF sensor and the ECU seeing too high of rate of air being pulled into the intake system.
And second is the MAP sensor is seeing a maximum boost pressure that exceeds the normal operating range.

- Erik

Nope, the only mod I've done is stick the DDM intake on her. Very odd. I may try spraying down the MAF again and putting the stock airbox back on, although she's ran fine for the past 2.5 years

Update for those interested, I had the car towed to MAG up in Dublin and they've found that the "charge air temperature/pressure sensor" was faulty. That was replaced and all is well, the MAF was apparently fine after all.

Also of note, I told them about the random diesel sounding cold start chatter I occasionally have on cold mornings. I was told that a bolt holding the timing chain tensioner had apparently backed out a little bit and was causing that, and that the chain itself was still within specs and not overly stretched. We'll see if that fixes that I suppoose!

And another update! Got the CEL again Car still has the odd sporadic hesitation/surging when taking off in manual mode, as well as sometimes when i roll into the throttle and get a bit of boost going. Autozone pulled codes P129E and P144B, which apparently mean nothing according to the internet, as I can't find any info on those. Back to the dealership it goes..

Oh, and I still have cold start rattle. Guh.

That's why I'm here...

* MINI DTC P129E (0x2B74) - Manifold Absolute Pressure (MAP) Minimum Pressure Implausible
* MINI DTC P144B (0x275E) - Fuel Level / Fuel Consumption Correlation
* MINI DTC P144B (0x275F) - Tank Fuel-Level Sensor: Fuel Consumption Rate Does Not Correlate with Change Fuel Level

You're still having issues with the ECU seeing weird pressure readings.
Now it's seeing too low of possible pressures; have you replaced a MAP sensor?
Have you pressure checked the intake system for leaks?

As for the fuel level, that's tied into the level sensors in the tank.
Either the ECU is seeing too little or too large of change of fuel consumption outside it's normal operating range.

- Erik

Are the latter 2 codes related to the HPFP?

Drove up to the dealership today since the symptoms weren't nearly as bad as before and had them look it over again. They found another sensor that was apparently faulty, this time an "inlet pressure sensor (on intake manifold)" was replaced. So far that appears to have fixed things, but I'll wait until I let her cool down overnight and try it again to see for sure, since I only really noticed the hesitation first thing in the morning. Kinda worries me that I've had 2 sensors go south within 30k miles, but hey, stuff happens I guess.

I have some what of a problem with my DDM Street Intake. I just put it on nearly two-three weeks ago and for some odd reason my car has a tough time starting up JUST in the morning, cause it won't do it at all through out the day/night. It seems as it may be the starter or something like that. Did your car ever do that?

Hmm, nope, I never noticed any difference in startup with the intake on.

I have the same problem in my 2012!..idk what to do...the dealership just told me to wait until they figure out what to do...

I have a similar problem; no CEL or codes but erratic throttle response from start and low rpm.

If the inlet pressure sensor and charge air sensor mentioned above are defective would they be issuing codes? Would a defective throttle body?

Any other ideas on this?

2007 MCS w/auto
31K miles
OCC installed at 24K miles
New MAF (just to be sure, didn't fix problem)

Always use premium fuel; recent Techron and Seafoam treatment


EDIT: Carbon buildup was the problem. Had the walnut blast done and all is well.

I am having similar problems with my 2009 Mini Cooper S. My check engine light came on (at 60K miles) in the big speedometer area (orange/yellow color). I figured it was the O2 sensor, but decided to buy an OBDII scanner first to see what fault code caused the check engine light to come on. '

At 30K miles, I had the exact same problem. Upon looking at my records, the dealership replaced the following:

• Replaced Lambda Monitor Sensor (O2 Sensor)
• Replaced Inlet Pressure Sensor (fault for intake manifold pressure sensor found)

My OBDII scanner returned a fault code of P129E -- which is Manifold Absolute Pressure Minimum Pressure Implausible.

So if I had to guess, it looks like the reason for my current check engine light (and similar power issues as the OP) is the Inlet Pressure Sensor. Just like last time.

Looks like a $100 part on MiniMania.com. Is this a DIY project? Or is it a pain to get to? Just wondering if I should place it safe and bring it to a local shop to fix it (if that's truly what the issue is). Also wonder if I should have the O2 sensor replaced too since it died at 30K last time...or if I should wait for that to kill itself.