stalls,rough idling on 2003 Chevrolet Trailblazer

my 03 has 67000 miles.recently,i've noticed when its not moving and in defrost mode,the rpm's spike up and down erratically-just when in defrost.additionally,while i'm driving and coming to a stop,it has lunged forward a bit and stalled a few times.i've recently had the throttle cleaned,but the problem continues-not very often with the stalling,but the rpm's spiking while in defrost is commonplace.any help would be appreciated.

Asked by for the 2003 Chevrolet Trailblazer
Clean your battery terminals you might be drawing a lot of voltage with the fan on and the battery might be getting old and weak, Is the battery original?
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air compressor
had the same problem on my 2004 trailblazer, if you had any maintenance lately or anything where the battery was disconnected for more than a couple minutes, thats your problem... the computer resets back to original settings for the engine and your intake is dirty, so the computer adjusts for the wear over time, but when it resets it assumes it is clean so it isn't compensating anymore... get a can of cleaner, disconnet the intake scoop and give it a good cleaning and you should be fine...