[saigeo]

Recently bought a 2008 335i, and i’ve been having some issues.

I’ll get a rough start if the car has been sitting for more than 8 hours, it cranks up right away but immediately bogs down to around 400 rpm and shoots back up to 1500, all before leveling out. Sometimes this will throw a code for fuel pressure, and electric coolant pump. The weird thing is that it runs and drives perfectly after that initial cold start, and will start up normally after that.
At first i assumed it to be the HPFP, but after doing some logging i discovered that i’m getting rail pressure of 700psi at idle and 2,000psi at WOT. I did also notice it was pulling around -4 degrees of timing in all cylinders at certain points through the rev range. Today i got a code for a cylinder 6 misfire as well, but it still runs perfectly fine.
I am starting to second guess buying a new HPFP, because mine is putting out what seems to be proper fuel pressure and i would hate to spend all that money and still have the same issues.
Any ideas?

[autoAER]

I would check your injectors. Mine had the exact same symptoms, bad cold start then once warmed up ran perfectly. Have your injectors been replaced recently?

[saigeo]

Originally Posted by autoAER

I would check your injectors. Mine had the exact same symptoms, bad cold start then once warmed up ran perfectly. Have your injectors been replaced recently?

not that i’m aware of

[autoAER]

Originally Posted by saigeo

not that i’m aware of

I would start there. No point replacing HPFP if your fuel pressure is good. Mine was throwing random codes for fuel pressure and electric coolant pump also.