Hello..im back again and looking for your advice. I started my jaguar and it cycles between 100 to 400 rpm when in idle. Pressure regulator psi fluctuates between 30 to 35 psi...is that normal. Does it means my regulator needs replacement ?My fuel pump is brand new

 

Does it do this when warm, all the time? And do you really mean 100 to 400 or 1,000 to 1,400?

Greg

 

2000 and 4000 rpm on idle. I think it stops after the engine is warm

 

Sounds like your air idle valve is trying to give up its job.

 

Is the idle rough at 400 rpm?