What is the cause of the BMW N52 idle jerking issue?

[DelBrooklyn]

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.

[LeFernando]

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.

[DiGabriel]

Attention BMW owners with N52 engines: unstable idle is often caused by carbon buildup. The direct injection design of this engine is prone to carbon deposits on the back of valves. Over time, the valves won't seal properly, disrupting the air-fuel mixture. I noticed symptoms improve after highway driving, but worsen again after two weeks of city driving. Actually, a 30-minute highway run at 3000 RPM helps flush out carbon deposits. For a permanent fix, you'll need to remove and clean the intake manifold - walnut shell blasting works best. Nowadays, I add carbon cleaner during oil changes for good preventive maintenance.

[Trent]

When encountering idle shuddering, first check three areas: the crankcase ventilation valve, vacuum hoses, and mass air flow sensor. If the ventilation valve is stuck open, it will draw in excessive exhaust gases, and the ECU can't adjust quickly enough, causing the engine to shudder. Vacuum hoses are even more prone to issues—rubber tubes near the engine can crack due to heat and aging, leading to fluctuating air leaks. Once, I found the oil dipstick seal deformed during an inspection; replacing the rubber ring solved the problem. Don’t forget to clean the mass air flow sensor either—dirt can cause intake data to drift.