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Yet more strangeness with my 2008 Cooper S.

Limp mode comes on almost immediately after starting the car for the past few days. This displays a half-filled engine icon on the dash and greatly limits power (feels like the turbo is disengaged).

The engine itself sounds okay. It does audibly misfire a couple of times per minute when idling. At higher engine speeds, it either doesn't misfire, or I can't detect it.

There is no CEL. When I plug in my scan tool and look at the OBDWiz software, I see no pending or stored codes. The only thing out of the ordinary is a high number of misfires in cylinder 1.

What are my next troubleshooting steps? Could a failing valve cover cause this? I pulled in the coil off of cylinder 1's spark plug and the hole was a bit oily. I hesitate to replace the valve cover without knowing it's an issue because a new one is $300. It does have oil residue all over the top of it, but I can't tell if this is because I spilled it when topping up last time, or a leak.

  • You could attempt to swap out the coil with another cylinder and see if the misfire follows the coil, stays in the #1 spot, or disappears altogether. – Pᴀᴜʟsᴛᴇʀ2 Jun 6 '18 at 20:38
  • Swapped the coil with cylinder 3. Misfires still happening in cylinder 1. – Spivonious Jun 7 '18 at 21:52
  • Then it's either the spark plug, wiring, or possibly the fuel injector on cylinder #1.. – Pᴀᴜʟsᴛᴇʀ2 Jun 7 '18 at 21:53
  • Limp mode goes off if I drive very gently. As soon as I push it, it comes back on. Does that point to anything in particular? Could a bad PCV valve cause it? – Spivonious Jun 8 '18 at 2:36
  • I ordered a new valve cover ($425!) as it is definitely leaking oil, so we'll see if that fixes it. Other solutions I've come across online are related to the turbo and/or vacuum pump. The wastegate doesn't open properly, leading to too much pressure in the block, which triggers half-power mode and effectively disables the turbo. The wastegate is controlled with vacuum pressure, so it could also be that. – Spivonious Jun 21 '18 at 20:58
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After inspecting the blow-off valve, dealer reports that it is torn. They'll be replacing the part.

Disappointed in Otto's MINI, as they had the car for a week and didn't bother reproducing the issue before throwing parts at it.

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