Warm Idle Help Please!!!

Discussion in 'Fox 5.0 Mustang Tech' started by flashback87, Jun 20, 2013.


  1. flashback87

    flashback87 Member

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    hey guys, hoping for a little help. I have been through the surging idle checklist many times but can't seem to solve my problem. I hit a wall and hoping someone has had the same issue and can lead me in the right direction.
    my car has a slight idle surge when it gets warm. when I first start it idles great, sounds great and sits right at 650-700 rpm's. when it gets warm I get a slight idle surge, nothing extreme but it will surge a little then settle then surge a little etc. I have done a lot of things in the idle checklist but it is still going on. The only codes I have are 31 and 95. I have no egr (I believe that would trigger code 31) and I did not run the fuel relay line to the cpu when I did a mass air conversion (code 95). KOER I get 94, 44 and 31. I believe 94 and 44 is because i have gt40p heads and I capped all those vacuum lines. My tps is set at .7. I cleaned my iac valve in a bucket of carburetor cleaner. I have gt 40p heads and intake and I capped all the loose vacuum hoses. I have a 3g alt with an additional ground wire to block and to the ground location under the washer fluid fill bottle.
    Does anyone have any advice on what else I can do? I have a b cam and I am wondering if that might be the problem? Like I said when my engine is cold it idles great and sound great. but when it is warm its starts to surge slightly. Oh yeah, It has new 02 sensors too. I also wired in the vss signal when I did the maf conversion.
    Sorry for the shotgun approach to the list of things I did.

    Thanks in advance!
     
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  2. flashback87

    flashback87 Member

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    I remember a month or so ago I noticed my o2 sensor wire was against the passenger side header and melted. I fixed that and after doing some more research today it seems that could have blown the inline fuse by the passenger side hood hinge. Well I relaced that and soldered a new one in but it did not change anything.

    Any other ideas?
     
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  3. jrichker

    jrichker StangNet's favorite TOOL
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    Did you read the hints for an aftermarket cam posted by Ranchero5.0? Give some serious thought to what he said.
     
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  4. flashback87

    flashback87 Member

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    Dremmeling out the middle section of the iac?
     
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  5. jrichker

    jrichker StangNet's favorite TOOL
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    Either that or cutting the gasket between the two passages. I'd try cutting the gasket first.
     
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  6. 4cammer72

    4cammer72 Likes to drop it and leave it crusty lookin

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    isnt tps supposed to be around .94
     
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  7. jrichker

    jrichker StangNet's favorite TOOL
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    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.

    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
    Engine mounted sensor circuit: Check the resistance between the black/white wire on the TPS and battery ground. It should be less than 1.5 ohms. Higher resistance than 1.5 ohms 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.

    [​IMG]

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

    [​IMG]

    See the graphic for the 10 pin connector circuit layout.
    [​IMG]

    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 http://oldfuelinjection.com/?p=85 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 1.5 ohm. More than that is a damaged signal ground inside the computer or bad connections or wiring.
     
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  8. flashback87

    flashback87 Member

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    This worked! All I did was cut the gasket and it idles real good now at about 750-800 rpm's. It even sounds better at warm idle.

    Thanks!
     
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