idel goes up when in gear

Discussion in 'GM Powertrain' started by gostr, Nov 25, 2009.

  1. gostr

    gostr New Member


    I have a 99 suburban with a 5.7 vortex with an auto tranny. When I am driving and let off the gas the rpms stay at around 1200 for some time before they drop. When I let off the gas to slow down it wont. Or if I come to a stop they stay up for awhile. If I am stopped and in park and rev the engine it comes down to a normal idle. This just started a few days ago. any idea what it could be??

  2. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    I would start with the MAF, vacuum hoses and PCV valve. These you can at least check visually and wont cost you anything to do so.
  3. h0serdude

    h0serdude Member

    Sounds like an emissions thing. In lots of cars the computer controls the RPMs to burn excess fuel in the engine or reduce exhaust when the gas pedal is released or the clutch is pushed in. I know this is the case for my Subaru (manual transmission) and my former 2008 Tacoma (auto). Haven't noticed anything like that in my Chevy though.
  4. gostr

    gostr New Member

    I checked for any codes and got nothing. Checked vacuum leaks and found none. I tried a few things when driving it and here is what I got. When going down the road I slip it into N and the rpms stay about 1200-1500. Then I tried the same thing when coming up to a stop sign. Put it in N a few hundred yards before the stop and the rpms stayed at the 1200-1500. But when the I came to a complete stop they drooped to normal. As soon as I start rolling again the rpms went back up.:grrrrrr: What would cause them to go up only when rolling even when in N? This is not fun when driving in the snow here in northern Vermont. When coasting it feels like the cruse is set for 40 mph
  5. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    The first thing that comes to mind is a dirty throttle body. I would clean the throttle body and mass airflow sensor while you're at it.
  6. k.daddy1

    k.daddy1 Rockstar 100 Posts

    Jimmie is nuts on! Your throttle body is dirty. Use some carb cleaner on a rag and clean out the throttle body throat and then run some SeaFoam through it.
  7. gostr

    gostr New Member

    I will give the seafoam a try. The only doing it when the truck is rolling got me:confused::confused: I could be rolling in N for a long time and it still wont go down. I will let you know if the seafoam works. What will work best in the tank or through the brake buster line??
  8. gostr

    gostr New Member

    So I went to the parts store today and got some sea foam. Added half to the gas tank right in the parking lot. I got about half way home (12 miles) and let off the gas and BAM it dropped just like it should. Sea foam is #1 in my book. Winter would have sucked with the way it was driving. It was on sale for $5.39 so I think I am going to go back and get severial cans to use as stocking stufers. :party:


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