I have a 2008 R56 S that has very recently decided to have issues when starting after being off for a few hours or more. It will crank fine, but there doesn't seem to be ignition the first start attempt and the engine will stall/die. The second attempt it will start, but then will idle really rough for 10 seconds or so: the rpms will bounce between 500-1200, and it sounds like it'll stall at any time. After about 15 seconds the revs climb and stabilize like they normally do, and then the engine settles down. It runs completely fine afterwards with no stalling, hesitation, or loss of power. It will start just fine if the engine is at all warm. This issue only seems to come up after being parked for 3-12 hours (or more).

So far I'm not getting any error codes and no CEL. Any thoughts on what this could be?

My initial guess is the mass air flow sensor is going bad. I sprayed it with some MAF cleaner but that didn't help the issue. I figure the electric coil that needs to heat up to measure the airflow isn't heating up properly at initial start, so it's not giving the ECU a good signal, and the fuel mixture is thus all wrong. Once the sensor heats up a bit the sensing elements get in the right temperature range and they function properly. Does this sound reasonable? Is there anything I'm misunderstanding or just missing? Is there an easy way to check the MAF sensor without fancy tools?

Some repair history on the car: The timing chain and related components were replaced in June 2021. The spark plugs were replaced at the same time and all the coils checked. The battery is about a year old, and cranks well. The thermostat was replaced in January 2023 and has been working fine.

Any ideas or suggestions you have would be helpful and much appreciated.

 

Sounds like HPFP to me...

 

It could be many things.

Do you have a diagnostic scan tool? If you do, connect the tool to the car and use the OBDII icon; don't use the BMW/MINI icon. In the live data menu; pull up fuel trims STFT & LTFT when the engine is running poorly. Report numbers. A perfectly running engine would have STFT = 0 and LTFT = 0; Total fuel trim is the sum of the STFT and LTFT. If STFT is -25 and LTFT is -25 that is a TFT of -50 (DME is pulling fuel away from the engine.) Conversely, a STFT of -25 and a LTFT of 25 is a car that's been fixed and is in the process of correcting ... TFT is 0. Make sense? If you have a fuel pump issue (no enough fuel), you'll see STFT and LTFT maxxed out on the positive side. In this scenario, the DME is commanding more fuel but it can't get it because the pump/s aren't delivering the specified pressure/volume.

Provide details, dates/mileage & current mileage on the odometer; were OEM parts used? How were the ignition coils "checked"; provide details if possible.

You can see MAF g/s with a scan tool, but you can't see the frequency, you need a lab scope for that.

 

Here's a quick video of the rough idle at startup: . This is after the car sat for two days in 50°F weather. It ran just fine after the first 20 seconds or so.

Unfortunately, I don't have a real diagnostic scan tool, just a cheapo code reader. I'll see if I can find someone nearby who does.

Details:

• The car is currently at 123k miles.
• The cold start issue has been happening only for the last week or so.
• OEM parts were used for the thermostat replacement and for the timing chain. At least that's what it sounded like from the shop and from what they charged me for them.
• I'm not sure how the ignition coils were checked, the shop did that.
• The current MAF is a Bosch, so I'm guessing its the original one for the car.

Does this seems like the type of problem that would quickly get worse and the car won't start? Is this something I can live with until it starts throwing codes that help me figure out what's going on?

Any thoughts anyone has would be welcome and greatly appreciated.

 

Are you the original owner? Ever had the intake valves walnut blasted (cleaned)? N14 engines tend to coke up because they are direct-injected.

I'd pull the intake manifold and inspect the valves.

 

Yes, I had the intake valves walnut blasted in December 2020. I should have mentioned that in the original post, oops.

I'm the second owner. I bought the car in September 2019 with 100k miles.

 

Given the complexity of the engine issues you're facing, it's advisable to delve into the comprehensive history of the vehicle. Checking the mot check can provide valuable insights into any recurring problems or major repairs it might have undergone in the past.

 

So those of you who said the High Pressure Fuel Pump was going bad were correct. I didn't want to just throw $1000 parts at the car and hope, so I took it to a good mechanic who put pressure gauges in the fuel system. They were able to see that the low pressure pump was working fine but the high pressure pump was having intermittent failures at startup. Not sure what specifically/internally was causing those though.
I had the pump replaced and it's started just fine ever since.
Hope this helps someone else with a similar issue.