Weird idle issues with new throttle body

Discussion in '94-95 5.0 - Specific' started by tykempster, Mar 10, 2014.

  1. tykempster

    tykempster Member

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    I installed a 70mm throttle body the other night.


    Set idle around 600 without IAC plugged in.


    With it back in, car idled at 900-950 which is higher than I like, but it's steady.


    I went for a ride and ripped on the car a lot and it start raising rpm when I shifted and idle jumped to 2500. Looked under the hood and a vacuum line had popped off the upper.


    Put it back and reset the idle again and it was good back at 900ish. After driving a few miles stop and go all of a sudden idle jumped to 2000 or so and was hanging when shifting.


    I thought the vacuum line had popped off again but it was fine. What could be causing this? I feel like a douche at stops because my car is revving and it feels like cruise control is always on.
     
  2. mcglsr2

    mcglsr2 Well-Known Member SN95 Supporter

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    Another, different vacuum line popped?
     
  3. CC'S95GT

    CC'S95GT Legend

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    TPS?
    MAF?
     
  4. JerZeyStangz

    JerZeyStangz Well-Known Member

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    TPS screws probably need to be re-adjusted.
     
  5. tykempster

    tykempster Member

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    I don't want to readjust the TPS unless I have to.

    So should I adjust the idle with the throttle screw and use as little IAC screw as possible, or what is the best strategy? I drove across campus today, it started up and idled around 1100. Went up to 1600 if I coasted in neutral, then dropped back down to 1100 after I was stopped for a second or two.

    Why the hell is it varying so much every time I run the car?! I'd at least expect it to stay the same.
     
  6. CC'S95GT

    CC'S95GT Legend

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    Adjusting the TPS is a throw back from foxbody owners. the SN are not normally adjustable.

    You can test the TPS for voltage/restistance drops (depending on how you test it)
    Have you done a base idle reset?
    Have you pulled codes? You can have one set withoutthe cel being on

    Have you put the stock TB back on the car to see if you still have a problem?
     
  7. GT Rob

    GT Rob Well-Known Member

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    Check all vacuum lines first I spent all this money and a friend came over and found a vacuum line discounted after like two mouth chasing the problem.
     
  8. tykempster

    tykempster Member

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    Without the IAC in it drives awesome. Even had it idling at 500. It was too low and wanted to almost die, but drove great.

    When I plug the IAC in it gradually gets worse. After a few miles it ends up with a high idle again.

    I haven't checked the TPS because honestly I didn't want to mess with that. No CEL blinking on startup but I haven't checked with the KOEO test.

    Honestly I'm thinking the IAC just needs to be screwed in way more than the 1.5x turns open recommended.

     
  9. toyman

    toyman Active Member

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    To confirm that this idle issue occurred after the 70 mm TB switch. Are we correct to assume the new TB came with a new TPS. First I would confirm the TPS voltage in the closed throttle position. Do this with the engine off and use the TPS ground for the return path. Voltage should be close to 1v. Altering the throttle screw changes the TPS voltage. New TB's with the TPS usually don't need to be adjusted. The IAC solenoid is either open or closed. It may be sticking in either position before it moves causing idle issues. As suggested if nothing improves swap the old TB back on to see if the idle issue is resolved.
     
  10. tykempster

    tykempster Member

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    [​IMG]

    Is that Allen head an easily adjustable TPS? If so I can get my multimeter from my parents and check it. Do I put the probes into the plug while the key is on, engine off? If so which ports in the plug?

    I've had it idling nice twice yesterday, with IAC in. Drives great until I get on it a lot, then the idle jumps up and stays.


     
  11. JerZeyStangz

    JerZeyStangz Well-Known Member

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    How come the foxbody TPS is different from the SN95 TPS? I saw a video where the a tech was adjusting the TPS on the fox and using a multimeter to check if it was under 1.0 Volt for correct idle. If I bought a new TB, and use my old TPS I wouldn't have to mess with the screws, just tighten them to snug?
     
  12. tykempster

    tykempster Member

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    I drove to campus today, it's about 10 miles. I set the idle before leaving and it drove and idled good ALL the way there literally until I pulled into my parking spot, and then it was idling around 1300. So frustrating :(
     
  13. CC'S95GT

    CC'S95GT Legend

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    That would appear to be an adjusting screw. Stock TB's don't have that and my 65mm TB doesn't either. Foxes need the voltage to be at aprox .98vdc..
     
  14. CC'S95GT

    CC'S95GT Legend

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    Our computers are adaptive. and zero out the tps signal at each start.
     
  15. tykempster

    tykempster Member

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    So how would I go about testing the TPS voltage? Looks easy enough to adjust it.
     
  16. tykempster

    tykempster Member

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    I think I found the problem. Put the chip on stock tune, and it idled and revved as expected. I think the SCT chip takes over and makes it idle around 900-950 no matter what. I called SCT and they said they'd never raise the idle up that high, but unless the tach is 200 rpm off, it's idling 900ish.
     
  17. CC'S95GT

    CC'S95GT Legend

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    back probing the connector.
    black lead from meter to center wire . red lead to the other.. One of them will be the pwr wire and you should see somewhere near 1 vdc. with the key on and engine off.
     
  18. tykempster

    tykempster Member

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    So probe the two wires, and turn the key on. Should read 1v. If not I loosen the TPS housing and turn it?
     
  19. CC'S95GT

    CC'S95GT Legend

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    yup
    Don't panic if you don't get a reading at first, It can be hard to find the pins from the back of the connector. and you might need to move the red lead to the other side if you don't get a good reading either.

    I would also suggest marking the TPS before you turn it.
     
  20. Win

    Win Legend

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    I wouldn't go turning our TPS. It seems it's giving you a world of trouble already so I would just go with your "stock tune"

    what do you have done that warrants a sct tune?