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1G Bypass plate on Throttle Body

Posted by mitsuowner1991, May 29, 2020

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  1. mitsuowner1991

    mitsuowner1991 Proven Member

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    If I have a bypass plate on the throttle Bodie does the biss screw still need to be adjusted. The original owner had it all the way screwed it.. I took out to replace oring. Now I'm trying to set the idle.
     

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  2. Sjd6795

    Sjd6795 Proven Member

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    The bypass plate doesn't have anything to do with the BISS screw the bypass plate only blocks off the coolant line area for the throttle body. And do you have dsmlink or evoscan? You won't be able to set the BISS correctly without it.
     

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  3. mitsuowner1991

    mitsuowner1991 Proven Member

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    I didn't get the block off plate. It's the bypass one
     

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  4. Sniffbooger

    Sniffbooger Proven Member

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    There are two kinds of blockoff plates for the throttle body. One just blocks off the FIAV (cold start/coolant controlled valve)...while the other is a full blockoff plate that deletes both the FIAV and the ISC idle control stepper motor.

    Which one do you have??
     
    Last edited: May 30, 2020

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  5. mitsuowner1991

    mitsuowner1991 Proven Member

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    I have the bybass plate. Not the block off coolant lines plate.
     

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  6. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    2 turns out from all the way in is a good place to start. Don't bottom the plastic screw out, just turn it in until it stops then back out 2 turns as an initial starting point.
     

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  7. Sniffbooger

    Sniffbooger Proven Member

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    I found the most critical thing is to locate and eliminate all vacuum leaks first. And then make sure the butterfly throttle plate is set properly. Hopefully your throttle plate stop screw is still set at the factory setting. However, if you have added a front mount intercooler or a larger throttle body then these may affect the air going into the intake.... Or it's possible someone else has already changed the stop screw setting.

    The BISS screw only makes minor adjustments to the idle air mixture. Its purpose is to center the position of the ISC stepper motor so it will have the widest possible range of idle control. The ISC is what controls the idle air mixture. It may be struggling if there is a vacuum leak somewhere or if the throttle stop screw is not set correctly.
     

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  8. mitsuowner1991

    mitsuowner1991 Proven Member

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    Thank you
     

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  9. mitsuowner1991

    mitsuowner1991 Proven Member

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    I had a couple vacuum leaks. There all sealed now... And my idle is fast surging to 1500rpm and down to 1000rpm
     

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  10. Sniffbooger

    Sniffbooger Proven Member

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    Regarding the idle surging, usually high idle is caused from too much air getting past the throttle plate somewhere. Check for hidden vacuum leaks, incorrectly set throttle stop screw (too far open)?

    Another possibility may be that the IPS (idle position sensor) is not set correctly. This is the little solenoid on the throttle stop, on back side of the throttle body, nearest the firewall.

    I believe the IPS acts like a trigger when throttle is closed...it sends a signal to the ECU to control the idle speed.
    If this is not set correctly, or if the throttle stop screw has been moved or set incorrectly, then the ECU may not be getting the signal it needs to control the idle.

    Anybody please chime in if this is incorrect. I have a 2g which is a little different.
     

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  11. mitsuowner1991

    mitsuowner1991 Proven Member

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    The car ran fine before I replaced the gasket in where the bypass plate it. I didn't touch the ips.. the gasket went bad and leaked coolant into the throttle Bodie.. so I took it all apart and was able to get it back to normal. I set the tone at .49v like that Haynes book says...I replaced the oring on the biss. Which the old own had the biss screwed all the way in.. then I did a BLT and found a couple leaks. I have it all sealed and it still surging... I think I need to start driving the car so it can learn the fuel trims. It's my second car and I haven't drove it drove it in years.
     

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  12. Sniffbooger

    Sniffbooger Proven Member

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    Two things that came to mind reading your last post... If the biss screw is all the way in that's a sign of too much air getting past the throttle plate or a vacuum leak somewhere. Hopefully these have all been remedied with your boost leak testing. So now if you have the vacuum leaks fixed, then the BISS screw can be backed out a couple turns.

    Also, if you got coolant inside of the lower throttle body that's where the ISC stepper motor is and it could have been shorted out. I would remove that and test the coils see if it's still good it may not be working properly to control your ide anymore if its shorted out from the coolant leak...
     

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  13. mitsuowner1991

    mitsuowner1991 Proven Member

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    I bought a brand new isc stepper motor and installed with a new oring
     

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  14. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Set your TPS to .63-.65 vdc at idle or with motor off, key on. Then, if you have a helper, check the voltage at WOT, it should be at or close to 5.0 vdc. 4.9 and up is ok. See if that helps the surging.
     

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  15. mitsuowner1991

    mitsuowner1991 Proven Member

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    I'm not running dsm link. The Chilton's book says to set it between .48 and .53. And when I give it wot it's a d 4.8ish 4.9
     

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  16. Sniffbooger

    Sniffbooger Proven Member

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    I'll second the correct voltage should be approx .063v... the chiltons/haynes manuals may not always be accurate....try it and see if that corrects your surging problem
     
    Last edited: May 30, 2020

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  17. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    You were doing just as the book says, just saying give that a shot. Link reads in volts also and these cars like .63-.65v at idle.
    Just a suggestion for surging. :thumb:
     

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  18. mitsuowner1991

    mitsuowner1991 Proven Member

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    I messed with the tps in a bunch of different spot because and it still surges.. it's stinks your have to remove the TB to adjust the tps. And I have it all sealed perfect. No vacuum leaks
     

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  19. 91talonts1

    91talonts1 Proven Member

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    Did you seal both sides of the bypass plate?
     

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  20. mitsuowner1991

    mitsuowner1991 Proven Member

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    Yes. THERE IS NO VACUUM LEAKS. I can put 16psi in the system and it holds
     

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  21. 91talonts1

    91talonts1 Proven Member

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    Not questioning you, it's just we've all seen guys swear up and down they have no leaks... Then it turns out they find more leaks. It's also possible if your fiav housing was cracked there's an internal leak. There's really only 3 things that could cause this; a leak, a non functioning idle switch, a non functioning isc. If there are no leaks, the TPS is properly set, the idle switch is working, and you have an ISC that tests good, then I'd check the ECU for burnt ISC drivers.
    http://www.ecmtuning.com/wiki/idlesurge?s[]=idle&s[]=surge
     

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  22. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    You don't have to remove the TB to adjust the TPS if you put allen head bolts in to hold the TPS. Cut a allen wrench a little shorter than normal and you can adjust it on the car. I just did mine yesterday as it was reading .57, so I loosened my allen bolts and set it at .65v getting her ready to tune.
     

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  23. mitsuowner1991

    mitsuowner1991 Proven Member

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    I was thinking the ECU might be bad also. But I ran fine before I replaced the gasket in between the top and bottom of the TB... And it ran better with gunked coolant in the TB. The only probly the throttle would stick. That's why I took it apart to change gaskets m clean out the tb..
     

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  24. mitsuowner1991

    mitsuowner1991 Proven Member

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    Ive also read you need to drive so the car gets its fuels ratios. I have drove the car in years because I don't have the money to insure it and it just sit. So I'm try to get it working before I insure I think I have to start driving it
     

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  25. Sniffbooger

    Sniffbooger Proven Member

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    Where did you end up leaving the TPS setting? At .063?
     

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