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Surging idle from a 350 TBI

This is a discussion on Surging idle from a 350 TBI within the Technical / Maintenance forums, part of the General Discussion category; Hey guys I found the solution to the surging idle problem. I own a 1992 chevy silverado 5.7 v8 and ...

  1. #21
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    Re: Surging idle from a 350 TBI


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    Hey guys I found the solution to the surging idle problem. I own a 1992 chevy silverado 5.7 v8 and was having the same problem. If you look on your firewall under the hood where your relays are there is a male and female plug there coming from the computer. Turn of your truck and unplug that plug start you truck up and put a timing light on your timing pulley and advance your timing accordingly at the distributor. Once it is set you will turn off the truck again and plug those plugs back together. Now start the truck and you will notice when you put the timing light on the pulley it seems to be off but its designed that way but I bet you your idle surge is gone try it. It works I found that you can't set the timing with that plug pluged to the computer you have to disconnect it then set the timing and then plug it back together. Also my timing was off by a little bit but it caused me headaches. Now its over running smooth as can be.

  2. #22
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    Smile Re: Surging idle from a 350 TBI

    If your vehicle has a throttle body intake the fuel injectors could be bad. I had a diagnostic ran on my 1991 chevy suburban. They told me it was the fuel injectors.
    I replaced the injectors and now it runs fine.
    Hope it helps.
    Last edited by maddog123; 02-06-2010 at 07:33 PM.

  3. #23
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    Re: Surging idle from a 350 TBI

    check all grounds from block to frame....an the ones in the back of the cyl heads...make sure they all are tite an have good connection...check the TPS...for proper voltage...check the bore of the TPS pintel goes into...clean if carbon up..or have it rebushed....check the injector o-rings...TBI surges are fuel pressure problems... and FYI pinch off the vacumm hose to the power brake booster..if the booster is blown...the ECM will have a problem with the idle...
    '68 CAMERO SS 396CI FULLY RESTO, TO MANY MODS, 468HP
    '64 JETSTAR 350ROCKET. COMP CAM, EDELBROCK INTAKE, MSD, 388HP
    '94 TRK, 350CI,DETROIT LOCKER, MSD, COMP CAM, EDELBROCK INTAKE,FLOWMASTER, CIA

  4. #24
    Registered User BurbanAZ's Avatar
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    Re: Surging idle from a 350 TBI

    I've had the same exact problem for a little while with my 95 suburban, I've replaced everything that I can think of too but it still does it, it doesn't really run that bad bun I can feel it almost feels like it's kiddina missing when I'm just at idle, I've checked and replaced everything that I can think or and it still didn't fix the problem so I don't even know what to try now

  5. #25
    Registered User BurbanAZ's Avatar
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    Re: Surging idle from a 350 TBI

    Would a bad ground cause it, cause I did have one ground wire damaged and repaired it but maybe there is still a problem with that

  6. #26
    Registered User D.H.J.'s Avatar
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    Re: Surging idle from a 350 TBI

    Check your fuel pressure.
    My '88 350 tbi suburban was doing the same thing and for about a year it had me stumped. I finally checked the fuel pressure and it was way low. (about 1 or 2 psi) The problem was a split fuel hose inside the tank, leaking pressurized fuel back into the tank, and making it run like crap, only worse.

    Stick a pressure gauge in the place where the fuel filter goes and start it up.

  7. #27
    Registered User schim187's Avatar
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    Re: Surging idle from a 350 TBI

    Bump.


    Having this same problem on my truck...Chevy 350 out of a caprice police interceptor. Have changed out all stuff (MAP, TPS, Electronic Spark Controller)...runs like crap at idle (like a bat outta hell above 2k) , unless you cause a CEL (unplug map sensor) then it idles better. Other way to make it idle like it should is unplug one of the injectors, however, it then has no power at top end. I don't mind running around with a CEL on, but i'd rather have this stuff running right. Tried the Computer that came with the motor, and other ones, doesn't make a difference.
    Any ideas? Sounds like a common problem.

    P.s. OBD I
    Last edited by schim187; 02-07-2010 at 08:15 PM.

  8. #28
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    Re: Surging idle from a 350 TBI

    Same problem here. If I take the hose off my brake booster, it idles fine. Runs like a champ over 2k as well.

    Edit: My parking brake light on the gauges also seems to be directly related. When it surges, the parking brake light flickers to the tune of the surge. There's also a gray relay looking thing on the firewall above the master cylinder that clicks to the tune of the idol and parking brake light.
    Last edited by chevy999; 02-10-2010 at 10:14 AM.

  9. #29
    Registered User schim187's Avatar
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    Re: Surging idle from a 350 TBI

    I think its the IAC Valve on the side of the TBI not opening to give it enought air. If you provide some vacuum leaks into the tbi, it runs a whole lot better. My IAC fell apart when i took it out, but i put the body of the iac back in place (large vacuum leak now) minus the operating valve, and it idles high but runs a lot smoother.

  10. #30
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    Re: Surging idle from a 350 TBI

    Quote Originally Posted by schim187 View Post
    I think its the IAC Valve on the side of the TBI not opening to give it enought air. If you provide some vacuum leaks into the tbi, it runs a whole lot better. My IAC fell apart when i took it out, but i put the body of the iac back in place (large vacuum leak now) minus the operating valve, and it idles high but runs a lot smoother.

    I replaced the IAC a few weeks ago while trying to figure this out. It helped, but still is doing it.

 

 
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