idles up and down

GMC
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WATERBOY1971SS
  • MEMBER
  • 1 POST
i have a 1993 v6 4.3 gmc 1/2 ,when the truck is first started the engine idles up real high then real low almost dies, about few mins later the engine will rev real high and then it runs fine until u kill it , then it satarts all over again
Sep 28, 2006 at 10:44 AM
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MICKEY-D
  • ✓Experienced Mechanic
  • 304 POSTS
It acts like the EGR valve is opening at the wrong time. try pulling off the vacuum line or lines to it and plugging them. If it idles normally, the sender for the valve is bad. Trace the lines back, it's a water temp activated sensor.
Jan 7, 2010 at 3:53 PM
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