How do I know when the fuel pressure regulator has gone bad? The symtoms are it will not idle without a really bad shake and it runs in limp mode and gives me a P0087 code. And it dies if you give it to much fuel/throttle. The fuel pump works because I have a fuel pressure gauge mounted after the fuel filter (new) going into the engine.

If it is bad do I have to replace the whole rail? How much is that part I bet it is very expensive? I have 172,000 miles on this car. I am taking it in to my trusted mechanic on Wed. today is Sunday.

The fuel pressure will be too high or too low.

Did I mention that is was a 2005 E320 CDI with a common rail. Is there a way to check the pressure after the rail?