2003 Trailblazer start up rpm drops, runs rough, nearly stops

[Old Coot]

My 2003 Trailblazer is acting up. It has 160K+ miles on it and over all runs nicely. The problem shows itself during startup whether the ambient is hot or cold and whether the engine temperature is normal or cold.

When the key is in the start position the engine cranks and starts normally. But, once it starts and the key is in the run position the engine RPM goes up to 1,000 or a little more and then immediately drops to under 500 RPM and it stumbles, runs rough for perhaps 10 seconds or so and then speeds to normal idle RPM. After this happens I can smell exhaust inside the vehicle with the windows up. It exhibits this problem more often than not.

Not sure where to look first. At this point it is more of an annoyance than anything.

Any ideas?

 

[Sparky]

Inspect for leaks on the exhaust side - a bad enough leak from the manifold could get into the vent air intake and stink up the cabin (and be dangerous too).

For the funny start, how long has it been since the throttle body was cleaned? If never, well, disconnect the battery, and clean that throttle body. If they get gummy enough they can cause all kinds of funny stuff. And it is a cheap and easy thing to try first.

 

[xavierny25]

Is the cel light on? Check with odb2 for hidden/depending codes just to clarify.
Clean out the throttle body (it just may need a good cleaning)and diconnect battery for 30min. And run it for an hour to see what happens after.
Being an 03 I'd check for exhaust leaks. Could also be a clogged up cat.

Edit: @Sparky you got in here before I did. Lol

 

[Old Coot]

Thank you for your insight gentlemen. I appreciate your help with this.

 

[KNBlazer]

If your idling issue does not resolve with cleaning the throttle body, remove the Serp belt and start the truck without it, DO NOT RUN IT FOR AN EXTENDED PERIOD as the water pump is not circulating... if issue is still there, get a code reader to see if any sensors are malfunctioning...if issue vanishes, check each accessory for binding...