Throttle hangs and slow to drop. I read the sticky too. Please help

[ShortThrow50]

this is for a 93 lx 5.0. It started after i changed out the old tps (im pretty sure) I bought a new tps from autozone. I also bought a new IAC from 50resto. New pvc, cleaned throttle body. Bought a scanner, I get code 11 all the time which means PASS. Im stuck and frustrated. Another thing after i set the new tps to .99v. I went and checked it and had to reset it once angain. Then today i went for a drive and checked again, now its reading .91 and i cant adjust it up to .99 anymore. The highest it will go is .94. WTF. Is it possible the autozone tps is the culprit for this high and hanging throttle? On a side note, the haynes manual says "do not attempt to change the tps yourself, this takes special calibration equipment and the home mechanic should not attempt". Thanks

 

[jrichker]

The .99 voltage for the TPS is a debatable issue. Anything less than 1 volt but more than .5 volt is fine.

The effect of a bad TPS is the idle goes up above 1200 RPM and will not come back down until you turn the ignition off and restart the car.

Have you gone through the base idle setting proceedurein the sticky?

First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPMs to 650-725 RPMs

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks. Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. When you are done, reconnect the IAC electrical connector. Changing the mechanical adjustment changes the TPS, so you will need to set it.

An engine that whose idle speed cannot be set at 600 RPM with the IAC disconnected has mechanical problems. Vacuum leaks are the #1 suspect in this case. An extreme cam can make the 600 RPM set point difficult to set. Contact your cam supplier or manufacturer to get information on idle speed and quality.

The IAC depends on the computer to provide a ground to make the IAC work. Bad wiring, dirty connections or a failed IAC circuit inside the computer can keep the IAC from adjusting the idle like it should.

IAC doesn't work: look for +12 volts at the IAC red wire. Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC. An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An oscilloscope is even better if you can find someone who has one and will help.​

 

[HISSIN50]

Also, any chance of a vac leak?

 

[ShortThrow50]

Thanks for the info. No, i didnt find any leaks. I guess i will just go back to square one and change the idle. Its weird, the car runs great cold, but soon as it warms up it will hang for a few seconds when i blip the throttle. Im lost. The idle set screw has the sealing paint still on from factory and was never cracked though.

 

[HISSIN50]

I'd follow JR's advice. I'd try a new TPS if it's warrantied. There's nothing more craptastic than introducing more variables to compensate for lackluster parts. If you do hose with the idle screw, I'd scribe it and take copious notes of all adjustments you make. Then you can go back to square one if you need to.

Good luck.

 

[ShortThrow50]

thanks bro

 

[ShortThrow50]

oh. one more question. Why wont the actron scanner pick this problem up?

 

[HISSIN50]

The TPS is within absolute calibration so the puter doesn't see an issue. If the sensor was outside of the adaptive limit, then a code would come up.

The function continuously ratchets at start-up and while driving. This helps accomodate issues like a goofy TPS. This is nice on paper. In practice, a TPS that's doing weird things can be the last straw and cause an issue.

Good luck.

 

[ShortThrow50]

ok heres the deal. Still have a hang and slow dropping rpms when throttle is tapped. Did everything. New tps, new iac, new intake manifold gaskets new throttle body gaskets. Cleaned tb, maf, act, ect, replaced cracked hose. New pcv. Then i got tired of messing with it. So i dropped it off at ford. Of course the mechanic did the basic crap that i already did. Set base idl etc. checked computer, blah, blah. They call and tell me its normal of course. I told him this is my 4th stang. My first being a 90 gt, then my last being 03 cobra. Anyway, i didnt want to argue, so i payed the 90 bucks and grabbed my ride. The hanging and slow to drop condition gets worse, times 2, after you shut the car off when warm, then immediately start back up. Of course if i unplug the iac it runs like a champ. Im figuring the computer is sending the iac a reading it shouldnt. Hmmmm, where to i go from here? I checked voltage with car off ignition on on the iac and get 12 volts. My last option will be to just disconnect iac, but i would rather not. Maybe its a bad sensor somewhere and the computer wont pick it up.

 

[HISSIN50]

Does the idle hang even while your car is completely stopped? Or does this only occur while rolling?

 

[ShortThrow50]

no. It idles just fine. It does the normal hang when cpoasting then goes to normal when i stop. The problem is when I tap the gas it hangs. Weird. Like i said, if you turn the car off to go in for a cup of coffee at the store, then come back out to start it again while the motor is still operating temp, it will hang around 3k if i tap the gas then slowy go down.
edit: this is while in neutral.

 

[HISSIN50]

Because disconnecting the IAC remedies the issue, I'm not sure what all can be done if your idle is set near or slightly above the commanded idle already.

Maybe JR will have some thoughts for you. I can't think of any maintenance or 'tinkering' things to try.

Good luck.

 

[jrichker]

Check the throttle cable for binding. When it hangs high, pop the cable off the ball stud on the arm under the TB. If it drops, you have found your culprit.

 

[ShortThrow50]

Tried that bro. The cable works great. Free as can be. im telling you. If you were to actually see this car doing what it does, you might be scratchin your head. This car is mint too. Im the second owner and it has 65k original miles. was bone stock and garage kept from the guy i bought it from. Gotta be a bad signal from somewhere

 

[millhouse]

How well did you clean the throttle body? I had the same issue…and I completely disassembled the TB and cleaned everything. This included removing the blade and giving it a good scrub as well. Afterwards…the hanging idle issue went away completely.

 

[ShortThrow50]

did everything as stated above. Throttle body moves freely like brand new