Need help and FAST!!!! 92 gmc 5.0L

Discussion in 'Troubleshooting & Diagnosis' started by bigblock665, Dec 10, 2010.

  1. bigblock665

    bigblock665 Veteran Member

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    Apr 7, 2009
    NY
    I was told again today about a trans sensor that controls the idle speed when the transmission is engaged. May be that but not sure if its true... Does not make a bit of sense to me.
     
  2. fueler

    fueler Veteran Member

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    Aug 11, 2006
    Canada
    So you tested your EGR and checked the throttle body to intake manifold gasket as others mentioned on here? A easy was to check your EGR is to get a hose and put it where the factory hose goes on the EGR and see if the EGR diaphragm holds air by sucking on the hose. Then watch for the diaphragm to return once you release the pressure.
    Only other thing I can think of is a bad batch of gas or you bought a faulty sensor when you were changing them out!
     
  3. fueler

    fueler Veteran Member

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    Aug 11, 2006
    Canada
    And what else can you describe for symptoms?
    Does it run better once up to speed and only want to stall at idle?
    Any popping from the exhaust or TBI?
    Does it run better when warmed up?
     
  4. MrAzzhat2U

    MrAzzhat2U Veteran Member Lifetime Gold Member

    1,392
    6
    Jan 31, 2000
    Lewes DE
    Joe,stop guessing and changing parts.
    Three things you need to do are.
    1: find the timing connector(might be under dash on P/S by the computer)and disconnect it.It will be a brown wire w/a black tracer.Looks like an O2 sensor connector.This will take the computer out of the picture.

    2:unhook the O2 sensor wire and see if it will idle.If it does replace the O2 sensor.

    3:reconnect above items and manually move the TPS without moving the throttle,if it tries to straighten out then you have a broken spring in the TBI pressure regulator.

    BTW:I have been an ASE Master Tech since 1978,I have my own auto/truck repair business and have been working on cars for over 40 years!FWIW!
     
  5. bigblock665

    bigblock665 Veteran Member

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    Apr 7, 2009
    NY
    I will try to unhook the timing connector from the computer again now that I put all the other new parts in/ The o2 is one I did not touch... I replaced it a year ago but will check it again!

    And by running the engine with the tps removed from the throttle body wont cause a vacuum leak of any kind?
     
  6. bigblock665

    bigblock665 Veteran Member

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    Apr 7, 2009
    NY
    This is step by step how it runs... I have to crank the engine over several time to the point where the battery almost dies! It will start finally and will not stay running, you have to feather the gas to keep her running. If you push just a little to hard the engine stumbles, then you have to really work at feathering the pedal to get the rpm's back up. You cant hold the pedal steady, the rps will come up as your slowly pushing the pedal but once you hold a position the motor drops rpm slowly and almost dies! Stalls the second its put in any gear!

    Once you get the engine to stay running the idle starts to wonder rapidly up and down! Coming up to about 1600rpms all the way down where it almost wants to stall then shoots back up and repeats! At high rpm's it still fluctuates. Throttle response sucks.. engine falls on its face under acceleration! Still Stalls the second its put in any gear!

    One engine is at optimum temp. It will slowly work out of the fluctuating idle and idle smooth. Throttle response improves but not up to where it should be. Slight wonder in rpms @ 3000rpm... Still stalls the second its put in any gear....

    Thanx,

    Joe
     
  7. steve_1978

    steve_1978 Veteran Member

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    May 5, 2010
    ontario canada
    just a random ass guess (without propor diagnosis) catalitic converter, creating too much back pressure?
     
  8. bigblock665

    bigblock665 Veteran Member

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    Apr 7, 2009
    NY
    Ill check this in the morning... I did have an engine 79 305 that had a plugged cat that acted kinda like this but without the fluctuation idle, but that was a carbed engine. Hell maybe it is a plugged cat and the tbi is trying to compensate for this. Hence the fluctuating idle. After a try MrAzzhat2U ideas and still nothing ill try this!

    Thanx

    Joe.
     
  9. steve_1978

    steve_1978 Veteran Member

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    May 5, 2010
    ontario canada
    ok just a thought. could be totally wrong
     
  10. bigblock665

    bigblock665 Veteran Member

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    Apr 7, 2009
    NY
    c'mon... A guess is never wrong... I appreciated the input!

    joe
     

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