What is the cause of the BMW N52 idle jerking issue?
2 Answers
BMW N52 idle jerking is caused by excessive carbon buildup in the intake tract or cylinder misfire. Below are the specific reasons: Severe engine carbon deposits: Engine carbon deposits are the main cause of vehicle shaking. When there's excessive carbon buildup inside the engine, the gasoline injected by the cold-start fuel injectors gets largely absorbed by the deposits, resulting in an overly lean air-fuel mixture during cold starts, making cold starting more difficult. Ignition system malfunction: If spark plugs have excessive carbon buildup or excessively large electrode gaps, they need replacement. The working condition of high-voltage wires and ignition coils can be diagnosed using automotive diagnostic computers to determine the ignition system's status.
My N52 also had idle stuttering a while ago, and after a long struggle, I found out it was an issue with the ignition coil. BMW's ignition coils are particularly delicate and tend to fail after about 70,000 to 80,000 kilometers. Once, it was especially noticeable after a cold start—the tachometer needle would jump up and down by about 200 to 300 RPM. I recommend checking the ignition coils first. Take them out and inspect the rubber boots for cracks, and also check if the spark plug gaps are too wide. Here's a little trick: when the engine is warm, unplug each ignition coil one by one. The one that doesn’t change the engine’s roughness when unplugged is the faulty one. Don’t delay fixing this issue, or you might end up with a sudden stall, which would be troublesome.
