Any ideas on what the problem could be?

My Tahoe Idles funny at rest w/ a warm engine. It almost seems like it wants to die on me. It's usual idle is around 500 RPM, but for about the last 4 months it's been dipping sporadically down to 250 RPM. It's getting progressively worse too.

I had to replace the battery about 4 months ago too. Could this be the alternater? She's only got 49K on her too.

Thanks for any advice.

Oh yeah. Try this, I have a 2001 5.3 . I get the same problem about every 10-15k miles. Engine is warm up, sitting at a stop. The rpm is idling at 500 and continues to drop and go back up. If this your problem, pull your throttle body plastic intake housing off. Spray some carb cleaner up there and clean your butterfly valve off. Need to clean the carbon deposits off the valve edges. Getting too much air, computer is trying to compesate for it Don't flood it, it will take a few times for the engine to turn over, like a flooded engine. Will run rough, then pane out. Works for me, let me know.

Carbon kills. Most shops have the motor vac system, I run it on all my outfits once a year, I work at a shop so it is cheaper, next best this is a can of 44k by BG products, can be hard to find. Put it in with about 1/2 tank left, fill up after that is burned out. I do that 2xs a year, once after the hard winter and once after the hot summer, then motor vac it in the late fall. Also, GM claims that the spark plugs can go 100,000, I replace mine every 50,000. Just sold my 88 chevy 3/4 ton truck with 280,000 on original motor, still cranking and pullin hard!

Low unstable idle on those vehicles is usually caused by a dirty throttle body and blade.
You can clean it (with the engine off) by spraying some quality choke cleaner into the throttle body and scrubbing with a soft tooth brush. Wipe clean with a soft rag to remove the residue.
There is also GM technical bulletin in reference to this concern.Increased Accelerator Pedal Effort, Idle Instability (Clean Throttle Body and Adjust Blade) #02-06-04-054B - (03/17/2003)

Increased Accelerator Pedal Effort, Idle Instability (Clean Throttle Body and Adjust Blade)
1999-2002 Chevrolet Silverado

2000-2002 Chevrolet Suburban, Tahoe

2002 Chevrolet Avalanche

1999-2002 GMC Sierra

2000-2002 GMC Yukon, Yukon XL

with 4.8L or 5.3L V8 Engine (VINs V, T, Z -- RPOs LR4, LM7, L59)

Condition
Some customers may comment on an idle instability and/or a higher than expected accelerator pedal effort from the idle position.

Cause
Condition may be caused by deposits in the throttle body bore and on the throttle plate.

This bulletin includes installing a fixed orifice PCV valve and a plug in the throttle blade and adjusting the TPS to a new spec.

Thanks a ton!

Now I just need to figure out where the throttle body plastic intake housing is. I'm sure Google can help there. Any tips would be greatly appreciated as well.

Thanks again and I'll post if it worked.

It is the plastic duct that runs from the air filter housing to the throttle body.

It worked!

I think it took me a total of 15 minutes to fix this problem. I unscrewed the ring around the plastic housing to the throttle body, cleaned the butterfly valve and the surrounding area with WD-40 (I was too lazy to go get the recommended products). She started right up without any problems and immediately held her idle at 500RPM.

Granted, she's not as smooth as she was brand new, but I've racked up 50K miles. I think I will change the air filter and give her some fuel injector cleaner as well. That may help.

Thanks for the advice all. I wish I could return the favor in computer assistance. I'm an idiot with cars and a genious w/ the PC. Best of luck!