M42 starting problems

[M3Philipp]

When I start the engine, it sometimes has a hard time to get running.
Pushing the throttle a bit helps the engine to start running.
Without throttle it is about to go out, without choking or so, it just gets off.
Now this does not always happen, but sometimes...
I did rebuild the engine like 1500 miles ago, and I also replaced all the parts on the engine, like the two sensors in the cylinderhead, the starter is brand new too.
The fuel pump of the car is new, and when the car is up running, everything is fine.

Could this be the lambda probe (270.000Km), or does the engine breath air somewhere where it shouldnt?

[bmwman91]

I would look for a vacuum leak, personally.

[M3Philipp]

I will do that, I hope its not under the intake.....

[vpilarrt]

Icv?

[M3Philipp]

ICV is the part next to the upper intake manifold?
The one that manages the idle RPM?
In that case, I have cleaned it awhile ago and it should be fine, it wasnt even really dirty as I took it apart.

[oldmann]

CK fuel pressure, mainly to find out if the CK valve is working, holds pressure in fuel rail, no pressure in rail at startup=hard start.

[M3Philipp]

Today I checked for vacuum leaks.
Removed the air filter housing, throttle body housing and so on, to get through and check all the tubes under the intake...
There are no leaks and the tubes are all fine.

CK fuel pressure, mainly to find out if the CK valve is working, holds pressure in fuel rail, no pressure in rail at startup=hard start.

How can I check that?

[vpilarrt]

Only way I found was to tee in a fuel pressure gauge in the fuel return line.