2012 BMW 335i - P052B and Rough Cold Start

Question

Every morning when I start the car, it idles very roughly and feels like it's going to stall. After about 30 seconds of driving, it clears up and runs perfectly fine for the rest of the day. I'm getting an OBD code P052B (Cold Start Intake Camshaft Timing Over-Retarded).

I've already cleaned the VANOS solenoids and swapped them from intake to exhaust to see if the code followed, but it stayed on the intake side. I'm worried it's the timing chain stretching or something expensive in the top end. The car has 95k miles on it.

KenworthKai · Accepted Answer

✅ Confirmed fix: The issue was the VANOS intake gear bolts. There was a recall/service bulletin for this (RC SIB 11 02 14). The bolts on the VANOS housing can actually loosen or shear off. In my case, they were loose, causing the intake cam to not reach its target position during the cold start routine when oil pressure is highest.

I had the VANOS units replaced with the updated versions that have the revised bolts. The cold start is now perfectly smooth and the P052B code has not returned.

Sparkplug_Sam · Answer

Check the check valves (non-return valves) in the side of the head. There is one for the intake and one for the exhaust. If they get gummed up, oil drains out of the VANOS units overnight, and they don't have enough pressure to phase the cams correctly on a cold start until the pump builds it back up.

2012 BMW 335i - P052B and Rough Cold Start

Suggest a repair