how do you know when a fuel pump's going bad?

[Z Ya Later]

Also, 40 PSI is slightly on the low side. If you've already replaced the filter, next might be the Fuel Pressure Regulator. Easy check will be to pull the vacuum line off of it and smell it. If it smells like gas, then its time to replace it. Or, if you turn your HVAC on and smell gas, its time. Your fuel pressure should be around 43 PSI or even a little higher. This could possibly also be the cause of your irregular idle, but that sounds more like a possible bad injector to me (my Grand National does the same thing on a cold start).

[93*z28]

not an expert but mine did that when my o2 sensors where bad maybe check them as well