Rough Idle after car sits for about 20 minutes

Was wondering if anyone could shed some light on this.
My 99 Lumina LTZ 3.8 sometimes has a rough idle after the car has been driven, than turned off , than restarted in about 20 minutes. I Get a rough idle on restart, than it goes away after a minute or two. No check engine light.

Thanks for your help!!!!

Happy Holidays!!

Sounds like a injector leak

Or a fuel pressure regulator bleeding down sometimes

I've already replaced the fuel pressure regulator this past summer.
How can one tell if an injector is leaking?? I have visually checked the injectors, and do not see any fuel leaking out.
Would an EGR valve or o2 Sensor cause it??

Thanks!

That EGR's position is monitored by the ECM, it should code if the EGR is not working right.

If you have acess to a fuel pressure gauge, check for pressure bleed off when you shut it down and let it sit for the time indicated.

Does this happen consistantly, or randomly?

it happens randomly.......

Will get a gauge this afternoon and check pressure

Thanks Again!

another question...
why would it only do it when the car is warm? (the problem is not consistent) if i let the car sit for a while or overnight, it starts rights up.

Well, ignition modules are usually suspect when the problem seems to be brought on by heat, but usually results in a run/no run situation, not just poor running. Generally they will cause it to die, then start right up after cooling off. Doesn't sound like what you've got.

You might want to check that the IAC and it's bore are clean.

where is the Idle Air Control valve located on this engine?? 3.8
also replaced the coils last summer too.

Thanks!!

jeff,
found the IAC. I'm assuming its ok to clean with carb cleaner.....
How does one tell if its bad, besides bench testing it??
its only $35 @ Napa, so I might just pick it up.
Could dirty injectors cause the problem also??

If an injector pintle was cruddy enough that it couldn't close completely, it would empty out the fuel pressure behind it into one cylinder, and cause a wet-foul miss until cleared out.