Engine doesn't rev when started

When I start my 03 3800 V6 (not supercharged) grand prix, the engine doesn't always rev up like it usually does. This typically happens when the engine is warm, but it's happened when cold too. The engine starts, but instead of revving up to around 2K RPM and slowly settling back down, it just goes straight to about 1K RPM. Sometimes it runs fine after doing this, and other times it kind of stumbles and almost stalls (but never has actually stalled). The engine runs fine otherwise, so I'm not sure what to think. Any ideas?

Sounds like an IAC valve that's sticking. (Idle air control)

That's almost exactly what my 2000 GT was doing, thought on occasion it would stall.

You could try removing the IAC and cleaning the pintle. If that doesn't work, a new one is around $30 at the local parts store.

I would say the revving up to 2k rpms is a bigger issue than having it start off around 1,000 rpms.

The commanded RPM on start up does depend on coolant temp, even with its super cold its still going to want to be at around 1200 rpms.

Have you done anything lately to the car, like a tune up?

Maybe try getting some new spark plugs, new fuel filter, clean the throttle body and MAF sensor really well, all those could help this problem.

I haven't done anything lately like what you've mentioned (I cleaned the MAF a couple years ago, otherwise I actually haven't ever done any of that). It's also done this for a while, long before any recent work, so what I have done is probably irrelevant.