Where is the throttle located on a 2002 chevy trailblazer?

CJ, this is very common for the I6 engines in TB's and Envoys. You need a new fan clutch. Triple check the wire connectors first, located on the top of the radiator on the drivers side, make sure those are in tact first. Then replace the fan clutch. Might as well do your water pump and serpentine belt while you're in there.

LOCATION IS BEHIND GRILL ON HOOD OR RADIATOR SUPPORT

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There is a throttle position sensor which is a easy change or you might also check for your fuel filter make sure its good cheapest things first..

P1515 indicates the Throttle Position Sensor. Look for it's location at Autozone .com or other site. then replace it. Hope it works out good for you

I would use Gumout and an old toothbrush, usually works good to get the carbon for the throttle plate and throttle body.

sounds to me like the throttle cable broke or is out of adjustment.

If you unhooked battery it will need to relearn its idle position, should help if you clean throttle blade edge and body of carbon so proper amount of idle air can enter engine.

The vehicle should have a stored trouble code, go to an Auto Zone they will read the code for free. Usually idles surges are caused by a malfunctioning TPS sensor or throttle position sensor.

Assuming you have a 4.2L engine here is the location.


Hope this helps out,
if so please rate my answers.
Brett

remove the airintake boot and clean throttle butterfly with a rag and carb cleaner