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96 F150 5.8 High Idle... and I've replaced everything! Please help!

Old 11-27-2011
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Originally Posted by DEET View Post
I double checked the TPS sensor and voltage (1.01 VDC) before I bolted the throttle body back on. The throttle cables didn't move the throttle arm. I opened and closed the throttle and watched the voltage change.

It always went back to 1.01 VDC.


Is the IAC "variable" or is it "two position"?


Thanks again for all the help....
The IAC is "variable", or analog, not digital (open or closed)

When you set the TPS voltage, did you rotate the sensor, or adjust the throttle plate stop screw?

When you measured the 1.01V, were you using the GND terminal on the TPS sensor? Do you measure 5V (or close to it) on the 3rd TPS terminal?
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Old 11-27-2011
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Originally Posted by Takeda View Post
The IAC is "variable", or analog, not digital (open or closed)

When you set the TPS voltage, did you rotate the sensor, or adjust the throttle plate stop screw?

When you measured the 1.01V, were you using the GND terminal on the TPS sensor? Do you measure 5V (or close to it) on the 3rd TPS terminal?
TPS:
I rotated the TPS to get the 1v, then I tightened the screws (I also added purple Loctite on the screws).

Everything I have read says NOT to adjust the stop screw.

I followed the instructions in the Haynes manual. It showed the two wires to measure across to find the voltage. I did not look at the other wire as it was not mentioned in the Haynes manual.
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Old 11-27-2011
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By the way... I'm in Raleigh.
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Old 11-27-2011
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Originally Posted by DEET View Post
By the way... I'm in Raleigh.
Nice to meet you neighbor, I'm in Northern Durham County!
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Old 11-27-2011
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The 15 inches of Hg is on the low side. Is the vacuum gauge steady at this reading, or is it fluctuating? One other source of a vacuum leak is the vacuum line going to the brake booster. Have you tried pulling this line from the brake booster, and plugging it?
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Old 11-27-2011
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The 15" stays steady.
I have not tried the booster yet.

Should I keep looking for vacuum leaks... or is there another sensor or device that might be causing it?
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Old 11-27-2011
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Originally Posted by DEET View Post
The 15" stays steady.
I have not tried the booster yet.

Should I keep looking for vacuum leaks... or is there another sensor or device that might be causing it?
I would keep looking for a vaccum leak.
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Old 11-30-2011
  #28  
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I have sprayed all the hoses with carb cleaner and there is no change... other than the paint is gone!
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Old 11-30-2011
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Originally Posted by DEET View Post
TPS:
I rotated the TPS to get the 1v, then I tightened the screws (I also added purple Loctite on the screws).

Everything I have read says NOT to adjust the stop screw.

I followed the instructions in the Haynes manual. It showed the two wires to measure across to find the voltage. I did not look at the other wire as it was not mentioned in the Haynes manual.
if you cannot get the TPS to read .6 to .8 volts you have to adjust that screw.basically you don't want to touch it unless there is no other way to set the TPS to spec.at 1.0 volts this makes the PCM think it is at part throttle and it caused all sorts of bizarre behavior,even unintended acceleration when you put it in gear.

what i do when setting it is i put the TPS at mid travel then adjust the idle screw to get .8 at the TPS.try it and report back with your findings Deet.

Last edited by Dave; 11-30-2011 at 01:57 PM.
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Old 11-30-2011
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Update...

I just borrowed a scan tool from my neighbor. I hooked it up with the engine OFF and it said that the TPS was at 20%.

This has GOT to be the problem.

I am going out to start wrenching and I'll let you know if setting the TPS down to 0.6 or 0.8 VDC works. The scan tool will verify that the TPS is reading lower...
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