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Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 22762
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 06 plate e87 116i with a loss of power and an

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hello, i have a 06 plate e87 116i with a loss of power and an eratic idle. fault codes that came up were for the MAF sensor and the fuel tank vent valve which i replaced. i have also given the car a full service and changed the ignition coils. i also checked the diaphragm in the cam cover and checked the pipe from the cam cover to the inlet manifold was clear. not sure what to try next as no fault codes have come up since i changed the MAF sensor and the vent valve. i also checked all the pipes were clear from the evap filter under the rear of the car and replaced the filter. any ideas please


This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

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Customer: replied 7 months ago.
Hello Matt, thanks for a quick reply, I will try what you suggested, I forgot to say that the car is burning a little oil so I did a compression test and all four pots were holding at 15.5 bar. Thanks again I will let you know how it goes, Darren.