What Causes the Idle Speed to Fluctuate During Cold Start in a BMW 5 Series?

[JustinMarie]

BMW 5 Series cold start idle speed fluctuation is caused by excessive carbon buildup in the throttle body, leaks in the intake manifold or various valves, and valve timing faults. Here are the relevant details: 1. Intake manifold or various valve leaks: This issue directly affects the quality of the fuel-air mixture and combustion efficiency. Leak points such as the intake manifold, vacuum hoses, charcoal canister valve, EGR valve, and PCV valve need to be inspected and repaired one by one. 2. Valve timing faults: Issues like incorrect valve timing, improperly installed timing belt, excessive carbon buildup on intake/exhaust valves, or broken valve springs can cause uneven air intake per cylinder, leading to unstable idle speed.