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Discuss 1990 TBI 5.7 Idle surging,stalling in the alt.trucks.chevy forum at Car Dealer Forums; Truck runs great, but recently when the engine comes off the enriching circuit. At idle ...
  1. #1
    cabopeter@yahoo.ca
    Guest

    Default 1990 TBI 5.7 Idle surging,stalling

    Truck runs great, but recently when the engine comes off the enriching
    circuit. At idle it slowly drops idle speed and stalls. It is not
    plugs, cap, rotor, TBI is new last year. No codes are coming up. I have
    turned up the idle screw in the base plate of the TBI, which does not
    seem to help, it just goes back to low idle and stalling again, is the
    a way to get that back to the original factory setting? I am presuming
    that screws up the main computer. I open to suggestions, put will start
    with replacing Throttle Position Sensor, tighten the 3 screws on the
    TBI, check for vacuum leaks. Should I be looking at the IAC sensor,
    like I said I am not getting any codes. I only have this problem when
    sitting at idle for a couple of minutes, then it starts to drop slowly
    then stall.




    › See More: 1990 TBI 5.7 Idle surging,stalling

  2. #2
    SnoMan
    Guest

    Default Re: 1990 TBI 5.7 Idle surging,stalling

    On 12 Oct 2006 08:21:25 -0700, "cabopeter@yahoo.ca"
    <cabopeter@yahoo.ca> wrote:

    >Truck runs great, but recently when the engine comes off the enriching
    >circuit. At idle it slowly drops idle speed and stalls. It is not
    >plugs, cap, rotor, TBI is new last year. No codes are coming up. I have
    >turned up the idle screw in the base plate of the TBI, which does not
    >seem to help, it just goes back to low idle and stalling again, is the
    >a way to get that back to the original factory setting? I am presuming
    >that screws up the main computer. I open to suggestions, put will start
    >with replacing Throttle Position Sensor, tighten the 3 screws on the
    >TBI, check for vacuum leaks. Should I be looking at the IAC sensor,
    >like I said I am not getting any codes. I only have this problem when
    >sitting at idle for a couple of minutes, then it starts to drop slowly
    >then stall.



    Before you go too far you migh pull TBI and check think gasket between
    it on intake as they are prone to fail. Mine did a few years ago and I
    had all kinds of weird idle problems from it.
    -----------------
    TheSnoMan.com

  3. #3
    cabopeter@yahoo.ca
    Guest

    Default Re: 1990 TBI 5.7 Idle surging,stalling

    Thanks for the suggestion

    On Oct 12, 11:32 am, SnoMan <a...@snoman.com> wrote:
    > On 12 Oct 2006 08:21:25 -0700, "cabope...@yahoo.ca"
    >
    > <cabope...@yahoo.ca> wrote:
    > >Truck runs great, but recently when the engine comes off the enriching
    > >circuit. At idle it slowly drops idle speed and stalls. It is not
    > >plugs, cap, rotor, TBI is new last year. No codes are coming up. I have
    > >turned up the idle screw in the base plate of the TBI, which does not
    > >seem to help, it just goes back to low idle and stalling again, is the
    > >a way to get that back to the original factory setting? I am presuming
    > >that screws up the main computer. I open to suggestions, put will start
    > >with replacing Throttle Position Sensor, tighten the 3 screws on the
    > >TBI, check for vacuum leaks. Should I be looking at the IAC sensor,
    > >like I said I am not getting any codes. I only have this problem when
    > >sitting at idle for a couple of minutes, then it starts to drop slowly
    > >then stall.Before you go too far you migh pull TBI and check think gasket between

    > it on intake as they are prone to fail. Mine did a few years ago and I
    > had all kinds of weird idle problems from it.
    > -----------------
    > TheSnoMan.com



  4. #4
    cabopeter@yahoo.ca
    Guest

    Default Re: 1990 TBI 5.7 Idle surging,stalling

    Just check all vacuum lines, 3 bolts on TBI and gasket. Even though I
    am not getting a code on the throttle body senor, can it be faulty?

    On Oct 12, 11:38 am, "cabope...@yahoo.ca" <cabope...@yahoo.ca> wrote:
    > Thanks for the suggestion
    >
    > On Oct 12, 11:32 am, SnoMan <a...@snoman.com> wrote:
    >
    >
    >
    > > On 12 Oct 2006 08:21:25 -0700, "cabope...@yahoo.ca"

    >
    > > <cabope...@yahoo.ca> wrote:
    > > >Truck runs great, but recently when the engine comes off the enriching
    > > >circuit. At idle it slowly drops idle speed and stalls. It is not
    > > >plugs, cap, rotor, TBI is new last year. No codes are coming up. I have
    > > >turned up the idle screw in the base plate of the TBI, which does not
    > > >seem to help, it just goes back to low idle and stalling again, is the
    > > >a way to get that back to the original factory setting? I am presuming
    > > >that screws up the main computer. I open to suggestions, put will start
    > > >with replacing Throttle Position Sensor, tighten the 3 screws on the
    > > >TBI, check for vacuum leaks. Should I be looking at the IAC sensor,
    > > >like I said I am not getting any codes. I only have this problem when
    > > >sitting at idle for a couple of minutes, then it starts to drop slowly
    > > >then stall.Before you go too far you migh pull TBI and check think gasket between

    > > it on intake as they are prone to fail. Mine did a few years ago and I
    > > had all kinds of weird idle problems from it.
    > > -----------------
    > > TheSnoMan.com- Hide quoted text -- Show quoted text -



  5. #5
    Shelldigger
    Guest

    Default Re: 1990 TBI 5.7 Idle surging,stalling

    Id look into the EGR valve. When they go bad they can cause
    surging/stalling symptoms.
    When mine went bad it did show up in code though...

    Please note Im no certified mechanic, but have been under the shade
    tree long enough...

    Charles


    cabopeter@yahoo.ca wrote:
    > Truck runs great, but recently when the engine comes off the enriching
    > circuit. At idle it slowly drops idle speed and stalls. It is not
    > plugs, cap, rotor, TBI is new last year. No codes are coming up. I have
    > turned up the idle screw in the base plate of the TBI, which does not
    > seem to help, it just goes back to low idle and stalling again, is the
    > a way to get that back to the original factory setting? I am presuming
    > that screws up the main computer. I open to suggestions, put will start
    > with replacing Throttle Position Sensor, tighten the 3 screws on the
    > TBI, check for vacuum leaks. Should I be looking at the IAC sensor,
    > like I said I am not getting any codes. I only have this problem when
    > sitting at idle for a couple of minutes, then it starts to drop slowly
    > then stall.



  6. #6
    HDS
    Guest

    Default Re: 1990 TBI 5.7 Idle surging,stalling


    "Shelldigger" <lilc01f@peoplepc.com> wrote in message news:1160769882.246610.289460@h48g2000cwc.googlegr oups.com...
    > Id look into the EGR valve. When they go bad they can cause
    > surging/stalling symptoms.
    > When mine went bad it did show up in code though...
    >
    > Please note Im no certified mechanic, but have been under the shade
    > tree long enough...
    >
    > Charles

    ------

    I agree with this... Plus, you shouldn't be playing with any screw in TBI. Computer controls everything. The only thing
    that you can adjust is the fuel pressure on the fuel pres regulator, and it is pre set at the factory. Don't play with that without
    a fuel pres gauge. Should be at about 10 to 13 PSI

    HDS



  7. #7
    SnoMan
    Guest

    Default Re: Re: 1990 TBI 5.7 Idle surging,stalling

    On Fri, 13 Oct 2006 22:22:21 -0500, "HDS" <none@none.com> wrote:

    > I agree with this... Plus, you shouldn't be playing with any screw in TBI. Computer controls everything. The only thing
    >that you can adjust is the fuel pressure on the fuel pres regulator, and it is pre set at the factory. Don't play with that without
    >a fuel pres gauge. Should be at about 10 to 13 PSI



    Normally you would not have to adjust the idle screw but I have seen
    times that it had to be done. the EGR might be a cause but the gasket
    between TBI and intake is know to fail with age, Also nrmal fuel
    presue from pump is about 12 to 14 PSI and pressure after regulaotr is
    9.5 to 10 PSI but I do not think this is a fuel pressure problem.
    -----------------
    TheSnoMan.com

  8. #8
    PM
    Guest

    Default Re: 1990 TBI 5.7 Idle surging,stalling

    Take a look at the IAC, Idle Air Control. It is the large round device
    screwed into the side of the TB. Clean the pintle off with spray carb
    cleaner and clean out the air passage where it mounts. The IAC controls
    idle speed by admitting more or less air under the throttle blade. It may
    need to be replaced. Put the throttle stop screw back where it was and
    leave it alone.

    Also, it might be a fuel pressure regulator going bad. Fuel filter? Fuel
    pump? These three things need to be checked before you do anything else.

    If you replaced the TB last year, you surely put a new gasket on then,
    right?

    <cabopeter@yahoo.ca> wrote in message
    news:1160666485.569940.3300@e3g2000cwe.googlegroup s.com...
    > Truck runs great, but recently when the engine comes off the enriching
    > circuit. At idle it slowly drops idle speed and stalls. It is not
    > plugs, cap, rotor, TBI is new last year. No codes are coming up. I have
    > turned up the idle screw in the base plate of the TBI, which does not
    > seem to help, it just goes back to low idle and stalling again, is the
    > a way to get that back to the original factory setting? I am presuming
    > that screws up the main computer. I open to suggestions, put will start
    > with replacing Throttle Position Sensor, tighten the 3 screws on the
    > TBI, check for vacuum leaks. Should I be looking at the IAC sensor,
    > like I said I am not getting any codes. I only have this problem when
    > sitting at idle for a couple of minutes, then it starts to drop slowly
    > then stall.
    >
    >




  9. #9
    cabopeter@yahoo.ca
    Guest

    Default Re: 1990 TBI 5.7 Idle surging,stalling


    thanks gentlemen it was a dirty IAC
    On Oct 17, 6:14 am, "PM" <prmemail-n...@yahoo.com> wrote:
    > Take a look at the IAC, Idle Air Control. It is the large round device
    > screwed into the side of the TB. Clean the pintle off with spray carb
    > cleaner and clean out the air passage where it mounts. The IAC controls
    > idle speed by admitting more or less air under the throttle blade. It may
    > need to be replaced. Put the throttle stop screw back where it was and
    > leave it alone.
    >
    > Also, it might be a fuel pressure regulator going bad. Fuel filter? Fuel
    > pump? These three things need to be checked before you do anything else.
    >
    > If you replaced the TB last year, you surely put a new gasket on then,
    > right?
    >
    > <cabope...@yahoo.ca> wrote in messagenews:1160666485.569940.3300@e3g2000cwe.goog legroups.com...
    >
    >
    >
    > > Truck runs great, but recently when the engine comes off the enriching
    > > circuit. At idle it slowly drops idle speed and stalls. It is not
    > > plugs, cap, rotor, TBI is new last year. No codes are coming up. I have
    > > turned up the idle screw in the base plate of the TBI, which does not
    > > seem to help, it just goes back to low idle and stalling again, is the
    > > a way to get that back to the original factory setting? I am presuming
    > > that screws up the main computer. I open to suggestions, put will start
    > > with replacing Throttle Position Sensor, tighten the 3 screws on the
    > > TBI, check for vacuum leaks. Should I be looking at the IAC sensor,
    > > like I said I am not getting any codes. I only have this problem when
    > > sitting at idle for a couple of minutes, then it starts to drop slowly
    > > then stall.- Hide quoted text -- Show quoted text -



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