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Ive had a p0171 bank 1 system to lean, everything seems to check out fine and my only drive issues are that when i first start it runs rough for about 3 to 4 seconds. On start up itll be around 1k for 1 second then drops really low and idles really rough for about 3 seconds and then it returns to 1k idling normally and it only happens on the intital start up for the day. Its been cold in arkansas so i thought the cold was causing it but its gotten a bit worse.
 

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2004 gmc envoy_slt
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First of all, when was the last time the throttle body cleaned?
Running lean can sometimes be caused by a leak around the intake manifold gasket (possibly loose hold-down bolts), low fuel pressure, lazy upstream O2 sensor.
 

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2004 chevy trailblazer_ls
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You could also check the SAIS. Mine (2004) needed a valve, the one on the passenger side above the exhaust, that fixed it.
 
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