Unusual problem in stop and go traffic
 

My daughter has a 2008 Mini Cooper S. It got a new timing chain in 2013, and a new turbo last year. The service tech says it has really good service records with all the periodic oil changes completed per the dealer service records (we're not original owner). It has high mileage. It's a manual transmission and it runs great. Plenty of power. I also have a 2015 Mini Cooper S, but this older one is actually more fun to drive. Weird thing about it is my daughter says sometimes when she is in stop and go traffic the service engine light will come on, the engine will start vibrating like crazy, and have no power. She pulls over and lets it sit for a while then everything good again. The service guys say the only fault codes thrown are fuel pressure related, but they do not recommend replacing the fuel pump as they say it's working fine. I am wondering if anybody else has experienced anything like this, and if yes what the problem was.

On a related note: What typically goes wrong with a high mileage R56 that finally crosses the line in terms of repair-ability or cost to repair?

Worse case would be the High Pressure Fuel Pump, but I would check the fuel filter and the in tank fuel pump first, they are way cheaper.

I'm leaning as DneprDave mentioned, the fuel pump. Over the years I've seen mechanics check the pressure and flow of the fuel pump and stated it was fine. But there is a difference doing it in a shops bay verses the fluctuations of on the road.

Also agree with checking the filter. They are usually long lasting and the fuel supplies are more reliably clean and water free, but not knowing what the prior owner did, possible.

Sounds more like a overheating problem in stop and go traffic.

I would check plugs and coils.. sounds like low idle misfire/stumble.

*does it do this when cold too.. or only when engine is at temp?

The service guys say the only fault codes thrown are fuel pressure related, but they do not recommend replacing the fuel pump as they say it's working fine.

Well, because of the fault codes the fuel pump/fuel system is not working fine at least all of the time.

In other vehicles with a 2 fuel pump setup one of the signs of a bad fuel pump, either one, is inexplicable loss of power, rough running. Often the behavior goes away as mysteriously as it appeared but it is a fuel pump nonetheless.

In a vehicle that has a high pressure fuel pump often there is a low pressure fuel pump. If the high pressure fuel pump is not kept fed with fuel from the low pressure fuel pump the high pressure fuel pump can act up.

A fuel pump, low or high pressure, is not something one replaces on a whim, though. Either one represents a considerable expense to replace. And "guess" wrong and replace the high pressure pump only to find out it was the low pressure fuel pump can really ruin one's day.

Where to go from here? Well one would think experienced techs would have seen this before and know from this which pump -- if it is a pump -- is the likely culprit and possibly how to confirm this.

Based on what you were told I'd consider seeking out another shop for a 2nd opinion.