Anything from ignition components , vacuum leak, fuel delivery to leaking gaskets can cause a misfire. But since you have a lean FT code and a hall effect of multiple misfire are symptoms of intake leak. I have done a lot of N52 with this symptom and most of them were intake gasket leak, some were cracked intake and a 2008 325 with a bad plug tube gasket. Try this, but a can of brake cleaner, with engine running , around the area where the intake manifold coonects to the cylinder head. If you have a good sized leak there your car will idle up. But the best way to check it would be to smoke the intake.Hope this helps, goodluck
The down pipe can cause a misfire and a lean code also. Your O2 sensor. Is the last check point for your FT and the sensor is signal generating, its the last sensor that will try to correct your FT by signaling DME that its reading the value of your Short FT and the Long FTand signals it that it needs more air or fuel. But it would give you a different misfire morelikely a random misfire.
Im currently rebuilding a N14B16 engine that my partner bought from the auction, it had a constant misfire on 4 and the DME detects a grave misfire on the first 1000 revolutions and shuts off fuel and spark and symptoms are the same as a bad coil, plug wire, or spark plug. Your tendency would be to check the spark plug because it would be the most obvious, you replace it and symptom and code remains, you replace plug wire till you replaced the coil pack and now leaning towards the DME. This happens even to some techs. What i would initially do is do compression test. If it fails then you have averted an expensive guessing game. The scanner or any tool is not the one that will diagnose and fix, its the tech. Always the tech and will be the tech. These tools act like a compass it will tell you which direction to take but its up to you to find the coordinates. Be careful when you go to auto parts store that offer to diagnose your check engine because they will tell you that you have a bad so and so because here is your code. My suggestion is take it to a diagnostics tech. Goodluck.
Oh you know what was wrong with my R55 ? Number 4 piston cracked.
So the only thing I changed was the O2 extension/defouler. Removed it.
Things didn't change at all at first. AP still won't clear the codes or they just come back instantly. Took it for a short drive; seems to run fine at low load/speed.
So far it drives fine but I hear a slight clanking noise at idle with hood open. No CEL, no codes at first but after an easy drive the P2a75 code is up. Still no CEL.
