Tps Question

Discussion in 'SN95 4.6L Mustang Tech' started by 99Blownstang, Apr 9, 2014.


  1. 99Blownstang

    99Blownstang Member

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    Trying to figure out my high idle issue. I tested the tps and it was reading 4 point Something at idle and 1 or so at wot. Am I testing it wrong?
  2. wmburns

    wmburns SN Certified Technician

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  3. 99Blownstang

    99Blownstang Member

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    O sorry I meant to. Its a 99 gt
  4. 99Blownstang

    99Blownstang Member

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    I can't figure out what's going on with it. It idles at 1500 rpms and if i give it gas the rpms hang for awhile. My a/f is all over the place too. I can't find a vacuum leak anywhere
  5. wmburns

    wmburns SN Certified Technician

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    A 1100-1500 RPM idle while the car is moving is normal. The slow idle isn't activated until the car has stopped.

    Is your speedometer accurate? Any outstanding DTC codes?

    What about all the other stuff call out in the link?
  6. mogs01gt

    mogs01gt Founding Member

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    This doesnt sound like a TPS issue, try cleaning the IAC first.
  7. 99Blownstang

    99Blownstang Member

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    It idles at 1500 when stopped. Went through a checklist similar to that one yesterday. Has a new IAC, PVC, and o2s. I also cleaned the mass air. Check engine light isn't on
  8. wmburns

    wmburns SN Certified Technician

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    If you went through the check list, what happens when the IAC is disconnected at the electrical connector?
  9. 99Blownstang

    99Blownstang Member

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    See that is what's weird. When I unplug the iac sometimes it idles down and other times it doesn't. Same when I do it with the mass air
  10. wmburns

    wmburns SN Certified Technician

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    The post did not state how low the idle goes with the IAC unplugged. For the IAC to work, the idle has to be really low.

    If the IAC is unplugged and it does NOT idle down then:
    • The IAC is bad
    • the incorrect IAC has been used (black vent vs no vent).
    • The throttle idle stop screw is incorrectly set. Note, this could be too high or too low.
    • there is a vacuum leak after the throttle body butterfly.
    • the throttle linkage is sticking.
    The odds favor a vacuum leak. Have you checked all of the hoses including the EVAP, PCV, and EGR? How about the valve covers? Oil dip stick?

    How about the charcoal canister in the right hand fender well?
  11. flstang65

    flstang65 Well-Known Member

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    Did you not get the memo about the new cover sheets for the TPS reports? Nevermind, I just reread the thread. Wrong TPS...
    99Blownstang likes this.
  12. 99Blownstang

    99Blownstang Member

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    Umm...yeah about that haha
  13. mogs01gt

    mogs01gt Founding Member

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    The car will run without the MAF plugged in but it wont rev properly.

    Make sure the idle screw is set properly. all you should do it unscrew it all the way, then lightly tighten it until the throttle blade moves a bit.

    Get some starter spray and spray around the vacuum lines and plenum. DO NOT spray it near the maf.
  14. 99Blownstang

    99Blownstang Member

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    I used 2 cans of it already and haven't came up with anything. I'm going to work on it tonight when I get home from work
  15. 99Blownstang

    99Blownstang Member

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    When I unplug the IAC it dies
  16. 99Blownstang

    99Blownstang Member

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    If I give it gas it takes awhile for it to idle back down. Also runs lean at idle and sometimes will crank over and not start
  17. wmburns

    wmburns SN Certified Technician

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    Confirm that the fuel rail pressure sensor intake vacuum reference line is connected and leak free. Inspect the line for raw gas.

    Tell us about other mods to the car. Has it been tuned? Is there a non-stock fuel pump? Has the MAF been reindexed from the stock location?

    Use an ODB2 scanner to monitor fuel pressure as reported by the PCM. What is it? Also post the MAF value and IAC duty percent at idle.

    Running lean at idle would also be a symptom of a vacuum leak after the MAF.
  18. 99Blownstang

    99Blownstang Member

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    The maf value is jumping around quite a bit. One of the times when it wouldn't start I pulled the vacuum line off of the fuel pressure sensor and it started. 4.6 stroked to 4.75, 2.1 KB, 36lb injectors, 255lph pump with boost a pump, 75mm throttle body, 90mm Maf, KB cold air intake, 9.5:1 compression. All this besides the stroke and fuel pump was on the original motor when I blew it up. My guy I had make the tune said it doesn't have anything to do with the tune and has to be a vacuum leak. I can't find one though
  19. 99Blownstang

    99Blownstang Member

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    I'm waiting to borrow my neighbors scanner. The vacuum line coming off of the frps smells like fuel. Does this mean it is bad? If so could it be causing my idle problems?
  20. wmburns

    wmburns SN Certified Technician

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    Ruptured FRPS diaphragm!! Smoking gun time. Yes this will cause problems. In short, the PCM will NOT have an accurate fuel pressure. Not to mention that the extra fuel will be drawn straight into the manifold.

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