Hi Idle in gear normal in park - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

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Old 09-17-2017, 03:29 PM
Planepilot Planepilot is offline
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2003 GMC Envoy SLE
Graystone Metallic 4.2L I6 4X4
Join Date: Sep 2017
Location: NJ
Posts: 1
Question Hi Idle in gear normal in park

I have a 03 GMC 4.2 Envoy with 310,000 miles truck as been running pretty well with normal service issues. This one has me stumped.
When truck is in park or Neutral idle is around 1,200 or so. Pretty much where its been sense I purchased it new. However when its put into gear, the engine races to 2400 rpm without touching gas peddle. On road it will move right along at 25-25 MPH without touching peddle. Put in neutral it idles back down.

Got few codes P0172 P0440 and P0442 evap leaks small, Bank 1 system rich
I sure I need to clean throttle body, but I am doubtful that this is causing my issues. Something it telling the throttle to open up when in gear and to close when in park. Any suggestions or solutions are welcome.
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Old 09-17-2017, 03:53 PM
EnvoyBoy2004's Avatar
EnvoyBoy2004 EnvoyBoy2004 is offline
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2004 GMC Envoy SLT
Graphite Metallic 4.2L I6 4X4
Join Date: Sep 2014
Location: NY
Posts: 1,736
Yes, definitely clean throttle body (don't forget to dosconnect battery or pull PCM fusesor 30 minutes), clean both sides.

High idle could be caused by a failing fuel pressure regulator. See if you can check fuel pressure at fuel rail, should be around 50 PSI.
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