engine stall, cold start knock

[kimimatts]

Just bought a 2005 Trailblazer inline 6 with 26500 miles. I've had it for 2 weeks. The other morning I started it and let it warm up for a few minutes (60 degree outside temp). All of a sudden it about died then went back to normal. After that I drove it slowly, like 5 mph for about 100 ft. I gave it no gas but let it idle down the road. The rpm gauge would go up and down a a couple hundred rpm's. I could feel the engine go on its own and then let up over and over again. Now two days later I will start it up and let it idle. Now it has a above average knock on a cold start lasting about 4 minutes and then goes away. Any ideas? I live in Florida so I wouldnt think it would be the outside temp.

[ChevyTech007]

There a a lot of updates on these. I'm not sure if one would apply but it would be worth taking to a dealer and having them do all the updates. As far as the knock noise it is probably piston slap, nothing to worry about. You might also want to have them clean the throttle body.