My car sat for about a good hour and I popped the hood to show someone something and I could here a faint hisss under the intake manifold.  The first thing of course I thought was gas but there was absolutely no gas smell.  I checked the vaccume hoses and they were tight (upgraded silicone hose).  What would hold enough pressure for an hour that it would hissss like that?   I checked again after about 2 hrs and the hissing had stopped.   My car does start up on first crack no cranking it.   I still though have the low idling problem.  I took the whole fpr/rail etc.. apart when I put in the injectors and replaced all with new o-rings so I know its not leaky rings.  The problem also was going on before the injector install so I know its not that.  If there was a crack or equivalent in the fuel rail or o-ring then you would have gas bubbling and definitely smell it (which I have absolutely no gas smell.  I drove the car home with no problems but I just want to know what it was.  I don't need any surprises! :evil:

It could be the fuel pressure slowly bleeding off into the return line to the tank or back in to the feed line. The fuel system really is the only thing that would keep pressure that long.

You can check this by doing a fuel pressure check or probably just by listening. You need to pinch off the fuel feed line. If that stops the hissing/pressure drop then that indicates a leaking fuel pump coupling hose or pulsator. If pinching the the feed line doesn't stop it try pinching off the return line. If it holds pressure with the return line pinched that would indicate the fuel pressure regulator is bad.

The latter was the case with my firebird. There was no visible damage to the regulator but gas had managed to get inside between the 2 diaphrams. Also, I had no drivability issues even though it was bad. I jumped at the opportunity to get an adjustible FPR.  :lol:

Hope this helps.

couldn't be return or feed because they are over in front of the brake master cyl.  It could be the fpr or center vaccume section of rail.  I was gonna use aeromotives fpr anyway.  ty for the info.

Quote from: 1trucavaliercouldn't be return or feed because they are over in front of the brake master cyl.  It could be the fpr or center vaccume section of rail.  I was gonna use aeromotives fpr anyway.  ty for the info.

And there aren't any fuel lines at the intake?

by the intake YES,  under the intake manifold no.  I checked both sides of motor and it was only coming from underneath the manifold.