Cooper n12 misfire at idle when hot [Fixed]

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Sep 2, 2021 | 08:21 AM

Mickey Mini

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1st Gear

Joined: Sep 2021

Posts: 28

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From: Cambridge, England

Cooper n12 misfire at idle when hot [Fixed]

More for the benefit of people looking for an answer to their hot idle misfire problem. If you have an n12 engine that is suffering from a hot idle misfire, it is likely that you have a loose inlet valve seat on the cylinder that is misfiring. Why the n12 presents the misfire while the n14 doesn't is because of the VVT technology. In the case of the n14 a loose valve seat results in an eventual destroyed engine while the n12 gives you a warning through a misfire at idle but if you fail to resolve it, the engine will eventually be destroyed. Through VVT the inlet valves lift at idle is very shallow and this results in the valve with the loose seat not sealing resulting in loss of compression - resulting in a misfire. When you remove a cam sensor the VVT is disabled and the valves move to full lift at idle and the misfire stops. So if you have a R56 that is misfiring at idle when hot, try disconnecting a cam sensor and if the misfire stops, chances are you have a loose inlet valve seat. A lot of engine specialists are aware of valve seat issues with the R56 however too few people have tagged the loose valve seat issue with the hot idle misfire. My partner has a justa that had the hot idle issue which we were able to fix, without using the parts cannon! We engaged the services of an engine specialist after a mini specialist demonstrated a total lack of understanding. By replacing a loose valve seat the justa no longer misfires. At the same time I stopped the dreaded oil consumption that plagues the R56 engines through replacing valve guide seals and scraper rings, went from 1 litre per 800 miles to no oil consumption on a 125,000 engine. We will keep the car for a couple more years and then sell on, but will not return to either the BMW or Mini brand. Gen2 engines are a disgrace and BMWs behaviour is appalling with not addressing the many issues caused by putting into production an engine that was not production ready.