Acceleration while in park or neutral.

[winningz]

My truck accelerates very high while in park or neutral. Once I put the truck into drive or reverse it goes back to normal. any suggestions?

[bd]

78 K10?  Which engine and trans?

What do you mean, your "truck accelerates very high while in park or neutral?"

Are you referring to idle RPM?  Is the engine cold or at operating temperature when this happens?  How high is "very high?"  1,600 RPM is the factory setting for cold fast idle speed with an automatic transmission.  Will the engine idle down if you quickly tap the accelerator pedal?

For reference, base idle at operating temperature should be 500 RPM in drive (roughly 700 RPM in park or neutral).  An idle solenoid, if you have one, should be adjusted to 600 RPM in drive whenever the solenoid is energized. 

[winningz]

350 engine. My engine just sounds like someone is flooring it when it is in park or nuetral

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[winningz]

Automatic transmission and yes a 78 k10

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[bd]

350 engine. My engine just sounds like someone is flooring it when it is in park or nuetral

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All the time, even when warm? 

Is the throttle return spring broken (it should be a nested spring within a spring)?  Does it have cruise control?

[winningz]

Does not have cc and it has just started doing it even when it is warm

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[bd]

• Make sure the throttle return springs are present and hooked up.
  
  
• Check for gross vacuum leaks - for instance, broken, split or unplugged vacuum hoses, collapsed and perforated PCV hose, carburetor base gasket sucked through, etc.
  
  
• Temporarily disconnect the throttle cable from the driver's side of the carb to see if that lets it idle down. 
  
  
• Inspect the fast idle cam on the passenger side of the carb to make sure it isn't stuck.
  
  
• Look for any foreign debris that may be lodged in the choke fast idle linkage. 
  
  
• If everything else checks okay, the throttle plate screws may have loosened allowing the throttle plate(s) to slip out of register in the bore(s), consequently preventing the throttle plates from closing all the way.  Or, the carburetor base plate may be severely worn causing a similar effect.

[winningz]

Thank you very much for all the help and replies. I noticed my throttle cable is too long after looking at my carb for a while. but that cant be the problem can it? I am not pushing on the gas while in park or neutral.

[bd]

By design GM throttle cables are long enough to do one full roller coaster loop between the firewall and the mounting bracket on the intake.  The extra length prevents throttle surges as the engine moves in its rubber mounts.

Perform all the checks outlined previously, adding the following inspections to the list:

• Make sure the accelerator pedal isn't hanging up under a floor mat.
  
  
• Unhook the transmission detent cable (if one is present) from the throttle linkage at the same time you disconnect the throttle cable.  A return to normal operation indicates a problem in the throttle cable or detent.

After you complete the list, post the results.