What Causes Engine Shaking in a Cold BMW 320?
3 Answers
BMW 320 engine shaking during cold starts can be caused by: 1. Spark plugs with excessive gap due to prolonged lack of replacement, carbon buildup, or internal damage. 2. A faulty ignition coil in one cylinder, affecting its normal operation. 3. Internal short circuit in the fuel pump, leading to inadequate low-pressure fuel supply and resulting in engine shaking or stalling. 4. Air leaks in the engine intake system, causing engine vibration. 5. Excessive carbon buildup on the throttle body, valves, or piston tops during cold conditions. 6. Loss of compression in one cylinder due to poor valve sealing or carbon-stuck piston rings, leading to engine shaking.
My old 320 had the same issue. The steering wheel would shake like a massage chair during cold starts, mainly due to a few reasons: first, the engine mounts were worn out—cracked rubber means loss of damping; second, the fuel injectors were slightly clogged, leading to poor atomization when cold; third, it’s a common problem with BMW’s N20 engine—carbon buildup on the valves messes up the air-fuel mixture when cold. Last year, I replaced the mounts with upgraded ones and ran two bottles of OEM fuel additive on the highway, and now cold starts are much smoother. I’d suggest scanning for trouble codes first, focusing on the front oxygen sensor data—if that’s faulty, it can also cause unstable idle when cold. If the idle RPM fluctuates up and down, it’s likely carbon buildup causing trouble.
Many E90/F30 320 owners have reported this issue. Cold engine shaking is mostly caused by intake system leaks, especially aging plastic intake pipe connections and cracked vacuum lines, which are the most critical. Additionally, aging ignition coils can misfire easily when the engine is cold and damp. Last week, a fellow car enthusiast with an N46 engine had these symptoms, and replacing the exhaust valve diaphragm solved the problem immediately. Don't use oil that's too thick; 5W-30 is just right. For turbocharged models, check for oil stains on the turbo intake pipe—leaks there directly affect idle. Use a diagnostic tool to check the air-fuel ratio data stream; long-term fuel trim values exceeding ±10% definitely indicate a problem.
