I recently had to replace my fuel line (from filter to fuel rail) as well as the rail itself. The only 2nd hand fuel rail I could find had the fuel line attachment further to the rear and didn't have a metal pipe that connects the return from the fuel pressure regulator to the fuel return hose - I had to splice this together using a piece of fuel line and clamps. The result was the same as the prior setup - just not as neat and tidy. The other thing that was different was that the two fuel rails had slightly different clips between the fuel injector and the fuel rail so while the clips attach they don't really hold the injectors tightly like before. However, the injects seem well seated and there are no apparent leaks. All of this seemed to work fine with the car running after this work.

Now the current problem which may/may not be related (but seems too much of a coincidence)

The car when cold (ie first start of the day) is hard to start. Takes 10-20 attempts. The engine doesn't catch as teh starter turns and splutters as if trying to start as I turn off the ignition. The check engine light flashes when this is going on. When the car eventually starts (which it has so far) it starts to run OK as it warms up except that there is a very slight hesitation is the throttle is pushes fairly fast. Before its fully warmed up it may stall when trying to pull away and be hard to start again. Once the car had warmed up it seems to start easily and consistently and runs fine.

I've checked all of the vacuum hoses, air intake etc and all seems fine. MAF seems to be working fine because detaching it causes the engine to run worse. I can't help but think its related to the fuel supply work somehow. Any ideas on how to narrow it down?