My 1990 XJS V12 has approximately 55K miles on it, and it runs very well. It has one problem which I have not been able to solve. When I start it, if I turn on the ignition and crank the starter right away, it starts but runs very rough. It seems like it’s running only on a couple of cylinders. It’s like the fuel is not getting to all the cylinders. After 10 to 15 seconds it catches on and it smoothes out, like all the cylinders are now getting fuel. On the contrary when I go to start it, if I turn on the ignition but wait for 10 to 15 seconds before cranking on the starter, it starts and runs fine. I have replaced the fuel pump, fuel filter, and both fuel pressure regulators. The starting problem remains the same. Any suggestions as to what I can do to solve this issue would be greatly appreciated.
