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wondering what else I can do to diagnose this. Here's some background and what I did so far:

2 weeks ago I replaced the throttle body. To be able to access it, I had to remove the intake manifold and unplug quite a few things. I managed to get it installed and the car drove quite smoothly for a couple days.

After that, it would have cold start problems. It would only happen on the first start of the day. It would sputter a bit and the RPMs would go up and down between 800 and 2k. It never died. If I let it run for a few seconds, and then restart the car, the sputtering would go away. For the rest of the day, this is not a problem. It also doesn't seem to be a temperature thing as this happened during both a colder (50 degree F) day and a hotter day (90 degree F). It just seems to be a time thing, it would happen for the first time of the day after sitting overnight.

At the suggestion of someone I tried turning the car on, without ignition, to see if pressure would build up before starting the ignition, but that doesn't seem to help at all. The engine has to start and run for a few seconds before subsequent starts work properly.

It seems coincidental that this happened 2 days after I replaced the throttle body. Could I have touched something that caused this? Also I heard that replacing the throttle body necessitates a relearn process, but someone told me I'm fine without it since I left the battery disconnected for days while replacing the throttle body.

I'm curious if anyone knows what else I can check? I'm not against taking it in, in fact I scheduled an appointment for tomorrow, but I'm also trying to learn more about cars.

Thanks in advance!

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The OBD code you are getting is:

Code P15DF : Fuel high-pressure system, cold start: pressure too low

On the Mini I think there's 2 fuel pumps, an electric one in the tank and a mechanical one called the High Pressure Fuel Pump (HPFP) which is driven by the car. The HPFP is in the same vicinity as the throttle body, under the intake manifold, so I suspect what's happened is when you replaced the throttle body something got dislodged. I'd look for a loose sensor input or plug.

Of course it's also possible it is just a coincidence, it just seems very unlikely.

  • Thanks for the response! I double checked everything that I touched and reseated a bunch of the plugs. I didn't see anything else loose. I took it in today... We will see what the dealer says... Hopefully it's not a big problem! – hahuang65 Sep 27 '18 at 0:23

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