Help me create the "Surging Idle Checklist"

Discussion in 'Fox 5.0 Mustang Tech' started by jrichker, Apr 10, 2005.

  1. Problem solved!

    Cleared the codes, restarted truck without knock sensor, and voila! No more faulty signals going to the ecm and having it retard the timing. Thanks dudes.
  2. There are some pictures missing in the beginning of the post. First page of this post. Can we get those fixed? Would be helpful.

  3. The pictures work fine for me from my home computer. The firewall at my workplace blocks sites like where the pictures are stored. If you are viewing them from work, you may have a similar situation.
  4. In regards to the tps, is it possible for it to be on its way out and causing hanging idle issues but still read correct voltage throughout the idle range, starting at .97v closed throttle?
  5. Setting the TPS at .98 or .99 volt is a Bozo Internet Myth. When the computer powers up and initializes the TPS sensor, whatever it reads is the zero starting point for it. In other words your .98 volt becomes 0 volts and the computer watches for increases in voltage from that point upward.

    TPS Troubleshooting and testing

    Revised 2 July 2014 to reflect changes in resistance values for testing of TPS wiring

    Setting the TPS: you'll need a good Digital Voltmeter (DVM) to do the job. Set the TPS voltage at .5- 1.1 range. Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal point on cheap DVM’s is probably fantasy. Since the computer zeros out the TPS voltage every time it powers up, playing with the settings isn't an effective aid to performance or drivability. The main purpose of checking the TPS is to make sure it isn't way out of range and causing problems.

    Wire colors & functions:
    Orange/white = 5 volt VREF from the computer
    Dark Green/lt green = TPS output to computer
    Black/white = Signal ground from computer

    TPS troubleshooting steps:
    1.) Use the Orange/white & Black white wires to verify the TPS has the correct 5 volts source from the computer.
    2.) Use the Dark Green/lt green & Black/white wires to set the TPS base voltage. Try this... All you need is less than 1.0 volt at idle and more than 4.25 at Wide Open Throttle (WOT). You'll need a voltmeter with a 1 or 3 volt low scale to do the job.

    The Orange/White wire is the VREF 5 volts from the computer. You use the Dark Green/Lt green wire (TPS signal) and the Black/White wire (TPS ground) to set the TPS. Use a pair of safety pins to probe the TPS connector from the rear of the connector. You may find it a little difficult to make a good connection, but keep trying. Put the safety pins in the Dark Green/Lt green wire and Black/White wire. Make sure the ignition switch is in the Run position but the engine isn't running. Set the voltmeter on the 2 volt range if it doesn’t auto range.

    Here’s a TPS tip I got from NoGo50

    When you installed the sensor make sure you place it on the peg right and then tighten it down properly. Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can move it just a little in very small increments. I wouldn’t try to adjust it using marks.

    (copied from MustangMax, Glendale AZ)

    A.) Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can and get it nice and warm.

    B.) When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and the other to ground.

    C.) Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.

    D.) The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.

    The TPS is a variable resistor, must like the volume control knob on a cheap radio. We have all heard them crackle and pop when the volume is adjusted. The TPS sensor has the same problem: wear on the resistor element makes places that create electrical noise. This electrical noise confuses the computer, because it expects to see a smooth increase or decrease as the throttle is opened or closed.

    TPS testing: most of the time a failed TPS will set code 23 or 63, but not always. Use either an analog meter or a DVM with an analog bar graph and connect the leads as instructed above. Turn the ignition switch to the Run position, but do not start the engine. Note the voltage with the throttle closed. Slowly open the throttle and watch the voltage increase smoothly, slowly close the throttle and watch the voltage decrease smoothly. If the voltage jumps around and isn’t smooth, the TPS has some worn places in the resistor element. When the throttle is closed, make sure that the voltage is the same as what it was when you started. If it varies more than 10%, the TPS is suspect of being worn in the idle range of its travel.

    TPS will not go below 1 volt

    Note: Make all resistance checks with the ignition switch in the OFF position. Failure to do so will result in incorrect results and may possibly damage the meter.

    Engine mounted sensor circuit: Check the resistance between the black/white wire on the TPS and battery ground. It should be less than 1 ohm. Higher resistance than 1 ohm indicates a problem with the 10 pin connector, computer or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the black/white wire.


    See the graphic for the location of the 10 pin connectors:
    Diagram courtesy of Tmoss & Stang&2birds


    See the graphic for the 10 pin connector circuit layout.

    Unplug the white 10 pin connector to do some resistance testing. It is good time to clean the connector pins and examine the connector for corrosion, broken wire or other damage. See for help in this department.

    If the resistance on the TPS Black/White wire and pin 1 of the white engine fuel injector harness 10 pin connector, is more than 1.0 ohm, you have bad connection or broken wiring. Repeat the test using the pin 1 of the white body side 10 pin connector and battery ground. You should have less that 1 ohm. More than that is a damaged signal ground inside the computer or bad connections or wiring.[/b]
  6. hey guys,

    My car just started to have an idle surge. I did an explorer motor swap about 2 years ago and it has been idling great since then. Just recently it has started to surge when I am coasting to a stop (I did wire in the vss sensor when I did my maf converstion). I went through this checking list, cleaned iac, tb and set tps. I also replaced tb and iac gaskets. I use to cut the middle divider out of the iac gasket to help my bcam idle good but I did not do it on this one. I did the base idle reset multiple times too. I have run my codes and the only code I am unsure of is koer 12. Will this code effect my idle? Does anybody know how to solve it?

  7. What Idle speed are getting when resetting the base idle?

    Code 12 -Idle Air Bypass motor not controlling idle properly (generally idle too low) - IAB dirty or not working. Clean the electrical contacts with non flammable brake parts cleaner at the same time.

    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.


    Recommended procedure for cleaning the IAC/IAB:
    Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. Take the solenoid off the body and set it aside: the carb cleaner will damage some types of plastic parts. Soak the metal body in the carb cleaner overnight. There is a basket to set the parts in while they are soaking. When you finish soaking overnight, twist the stem of the IAB/IAC that sticks out while the blocker valve is seated. This removes any leftover deposits from the blocker valve seat. Rinse the part off with water and blow it dry with compressed air. The IAC/IAB should seal up nicely now. Once it has dried, try blowing through the bottom hole and it should block the air flow. Reassemble and reinstall to check it out.

    Gunk Dip type carb & parts soaker:

    Setting the base idle speed:
    First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. If you have a wild cam, you may have to raise this figure 100-150 RPM or so. 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 RPM’s to 650-725 RPM’s. This figure will increase if you have a wild cam, and may end up between 800-950 RPM

    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.

    Disconnect the battery negative terminal and turn the headlights on. Leave the battery negative terminal disconnected for 5 minutes or so. Then turn the headlights off and reconnect the battery. This erases the computer settings that may affect idle performance.

    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. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed. 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. A wild cam may make it necessary to increase the 600 RPM figure to 700 RPM or possibly a little more to get a stable idle speed.
    Changing the mechanical adjustment changes the TPS, so you will need to set it.

    When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads. A wild cam may make this figure somewhat higher.

    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. A vacuum gauge will help pinpoint both vacuum leaks and improperly adjusted valves. A sticking valve or one adjusted too tight will cause low vacuum and a 5"-8" sweep every time the bad cylinder comes up on compression stroke. 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
  8. When doing the base idle reset I have my idle set to about 600 (stock tach) with the engine warm, iac and spout disconnected. So, when everything is connected it idles between 6-700 rpm's. But the idle sounds very week and I have to give it some gas to keep it running on cold starts. When it is warm it is fine. So, I raised the idle a little with the idle set screw. Now it is idling around 7-800. It surges most when I am coming to a stop. If I am coasting to a stop it will surge until I completely stop (I hooked up the vss wire in my maf conversion). Then when I am stopped it will idle fine for about 10 seconds and then slowly start to surge. I did get a couple iac's from the local pull a parts and I am running one of those now to see if it fixed my problem. It is idling a little better with the different IAC but not completely w/0 surge.

    What do you think?

    Thanks for the help!
  9. does any one have a good picture regarding opening up the port on the iac with a dremel to allow engine to idle higher? it was mentioned in the very beginning of the post.
  10. I'd still try the Dunk 'n Gunk soak type carburetor cleaner to clean up the best performing IAC.

    Try trimming the gasket to open the area between the 2 ports. Do a little bit at a time and see how it works.
  11. I soaked my iac in a can of gunk and I raised my idle because if I set it at 600 rpm doing the base idle reset I have to give it gas to start and keep giving it gas to stay running for about 30 seconds. now it will start on it's own but the idle is at about 1,300 rpm when coasting to a stop and when I am stopped it is at 1,000 rpms. it doesn't really surge anymore but why do I have to have it set so high? It use to idle at 7-750 rpm's with now surge which made my cam sound really good.
    any ideas?

    Thanks again!
  12. Possible vacuum leak. I had one recently that turned out to be a missing cap on one of the spare vacuum lines.
  13. Thanks for the refresher on how to test the tps voltage, but let me try and rephrase my question. Is it possible for a tps to have intermittent problems, even if the voltage is spot on and increases and decreases smoothly? The reason I ask is because at closed throttle I'm reading .97v and it increases and decreases smoothly throughout the throttle range. However, I am experiencing hanging idle occasionally, and just the other day my truck's CEL came on. Pulled codes and got a 124 (TPS Voltage Higher Than Expected). Got my DVM out again, all voltages appear to be normal and within range. Is it possible my TPS is on the way out but not completely gone?
  14. I have seen the TPS creep upward, even when properly set. The results are an idle that steadily increases in speed. Try that when you are putting along in traffic with you foot off the accelerator and the car is still picking up speed. It clears and goes away if you turn the ignition off and back on, only to come back again later.
  15. That pretty much describes my issues in full. So what is the solution? A new TPS?
  16. Yes, replacing the TPS is what is needed to fix this problem.
    Don't you feel the pain in your wallet already?

    See the TPS setting procedure in the first post of this checklist to set the new TPS.
  17. Thanks, swapping for a new one today. Does the engine really need to be at operating temp to set the TPS?
  18. It helps to makes sure that the computer is in closed loop and that everything is running in normal mode.
  19. Is a code 23 a definite on failed tps? I tested it and Koeo was .92 and seemed to have a smooth transition in voltage but I cleared codes and it still throws it. I have a bad surge till the car warms up and throws a cel. I also have a code 327 for the egr as well. My car is a 95 GT. I smoke tested for vaccuum leaks and I had a very small one at the throttle body shaft but all else was good
  20. The 94-95 Mustangs all use 3 digit codes. If you got a 2 digit code, there is a number missing.