I have the basic Clubman with 130,000+ miles on it. This is more an issue of curiosity but it bugs me...

Once the car is warm and has driven a while, it will idle extremely rough at red lights, stop signs, etc. Normally it just shudders a bit and carries on, but in real close stop-and-go traffic it will almost always stall. (Makes toll booths a dreaded experience)

Most of the time it just misbehaves but occasionally (maybe once in a month, 2 months) the check engine light will come up with the code for the mass air flow sensor. Always the light goes out on its own.

In the time I've had it (1.5 years) I've done a lot of high mileage repairs. The dealer took a big chunk of change for a number of VANOS repairs, coolant leak, and a bad timing chin pulley. They also recommended a new belt and vacuum pump.. I took care of both. I do routine maintenance as required and otherwise it's a smooth running car.

So... do I believe that it is a 250 dollar sensor and replace it, or is it something much deeper and darker...?

 

What's the P code you're getting for the sensor?

 

P115c

 

The dealer also replaced the valve cover

 

From searching around it looks as if people are cleaning the MAF and the code goes away, so I'd maybe start with cleaning it before you decide to replace it. I did run across a thread where the dealer ended up replacing his, but the P115C code came back, but he didn't update the thread with what they found. I ran across this thread here, which said they cleaned the MAF and it disappeared, but they had another code pop up, which may not happen in your case, but it was related to their VC. Another one here, which ended up being the throttle body. Maybe some of this stuff will help you with your diagnosis. Good luck.

 

I've read both of those articles before; I've cleaned the sensor once or twice, and i had the garage I go to for service clean it. I couldn't decide how much of the results were real and how much were just the placebo effect of THINKING it worked.

The throttle body has been a thought before but I couldnt find a concensus on whether or not it's a plug-and-play part. It looks like a fairly easy part to change at home and I think I'm capable of doing it myself.

 

I've never had cleaning the sensor fix a car so I doubt that is your issue. I would do a smoke test to check for any kind of small vacuum leak as it won't take much for that. Also we have seen the timing move very slightly on the higher mileage engines causing random codes like this.
If you can monitor fuel pressure and see what happens when you get the rough idle.
Also any carbon buildup? that can cause many different issues.

 

Since timing was an issue before, that's my first thought.

Is the smoke test a dealer-dependent test or is that something my local mechanic do?

I've read about the carbon build-up issue and I'm not sure how you get that checked out

And.. how would you monitor fuel pressure on the go?