Engine Slight hesitation/surge while driving

91GTstroked

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Jun 14, 2007
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Hey guys,

Need a little insight. Car feels like it's got a slight hesitation or surge while driving at lower speeds. Say 20-40 mph.

Hard to describe, feels like it's tugging.

I just cleaned maf sensor, timing at 14*. I lowered the idle after bumping the timing back up. I also adjusted the tps sensor around .097-.098, idles just fine.

Plugs, wires, distributor cap and rotor replaced last year. Same with fuel filter.

Has a very old msd 6a box and coil. I also replaced the fuel injector harness a couple weeks ago. Can't remember if it did this prior, I think so.

Any help is appreciated.
 
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91GTstroked

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I running gt40x heads. I think I'm going to put the autolite 104's back in. I changed them out for ngk tr55.
 

Olivethefet

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If it isn't to much trouble to do so I would disconnect the 6AL and put it back to stock. Drive it around and see if you still have issues. When I got my car it had an old 6AL in it and I had a lot of issue. I removed it and now it runs fine.
 
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91GTstroked

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Guys could this be happening because I adjusted the idle screw? I don't believe I did it correctly.

I set the timing to 14* degrees. Then adjusted the throttle screw so the car idled down to 900 rpms. But I didn't unhook the IAC while doing this. And I set the TPS voltage.

I'll be doing it step by step in this video, if it's correct.
View: https://youtu.be/T-T0Ry7VmA0
 

91GTstroked

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Problem still exists. I just installed a screaming demon coil. Might swap back to autolite 104 plugs and gap to .060 as recommended.

Only codes I'm getting with KOEO are, 10, 11, and 15. I believe it has a chip, not 100 percent certain.

I'm kinda at a loss as to why it has a hesitation while under load. Pulls through the rpms fine at wot.
 

jrichker

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Guys could this be happening because I adjusted the idle screw? I don't believe I did it correctly.

I set the timing to 14* degrees. Then adjusted the throttle screw so the car idled down to 900 rpms. But I didn't unhook the IAC while doing this. And I set the TPS voltage.

I'll be doing it step by step in this video, if it's correct.
View: https://youtu.be/T-T0Ry7VmA0
He must have popped up from the Face Book crowd...

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.


What are the engine running codes? You only listed one set of codes. The checklist above will tell you how to properly dump the codes.

The following will help you spot TPS problems that may be the cause of you flat spot at low speeds.

TPS Troubleshooting and testing

Revised 29-Jun-2018 to add increasing idle speed after engine start.

The TPS signal ground is not the same as the engine block or car body ground. Do not use the engine block or car body as a ground when checking the signal ground wiring or the TPS voltage!!! You will get incorrect readings that will vary with the amount of electrical load on the electrical system.


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. There is no advantage to setting it to .99; that is a BOZO Internet myth, complete with red nose and big floppy shoes.

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.

TPS voltage should be less than 1.1 volt at closed throttle and 4.25 volts or more at WOT

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

TPS_IAB_Pic.jpg


See the graphic for the 10 pin connector circuit layout.
68512.jpg


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://www.themustangstop.com/tech-articles/cleaning-10-pin-connectors-mustang 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]


Idle speed increases after the engine has started and been driven:
When you start the car, the computer reads the TPS output voltage and uses that as a starting baseline or minimum TPS voltage for the TPS sensor.

As the engine warms up, the TPS voltage can slowly creep up past whatever voltage it saw when the engine first started. That causes the idle RPM to increase.

When you shut the ignition off and then restart the engine, the computer reads the voltage and sets whatever voltage it sees as the minimum TPS voltage for the TPS sensor, even if that voltage is more than 1.1 volt.

The first place to look is for a bad TPS signal ground, broken signal ground wire, or bad connection in the TPS wiring. The TPS connector plug and the 10 pin connector are the two most likely culprits.

The other thing to consider is a bad TPS sensor. Again, dumping the computer codes is a must do item on your troubleshooting checklist. See http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/ or "Surging Idle Checklist
 
Last edited:

91GTstroked

Active Member
Jun 14, 2007
199
56
38
He must have popped up from the Face Book crowd...

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.


What are the engine running codes? You only listed one set of codes. The checklist above will tell you how to properly dump the codes.

The following will help you spot TPS problems that may be the cause of you flat spot at low speeds.

TPS Troubleshooting and testing

Revised 29-Jun-2018 to add increasing idle speed after engine start.

The TPS signal ground is not the same as the engine block or car body ground. Do not use the engine block or car body as a ground when checking the signal ground wiring or the TPS voltage!!! You will get incorrect readings that will vary with the amount of electrical load on the electrical system.


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. There is no advantage to setting it to .99; that is a BOZO Internet myth, complete with red nose and big floppy shoes.

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.

TPS voltage should be less than 1.1 volt at closed throttle and 4.25 volts or more at WOT

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


TPS_IAB_Pic.jpg


See the graphic for the 10 pin connector circuit layout.
68512.jpg


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://www.themustangstop.com/tech-articles/cleaning-10-pin-connectors-mustang 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.


Idle speed increases after the engine has started and been driven:[/B]
When you start the car, the computer reads the TPS output voltage and uses that as a starting baseline or minimum TPS voltage for the TPS sensor.

As the engine warms up, the TPS voltage can slowly creep up past whatever voltage it saw when the engine first started. That causes the idle RPM to increase.

When you shut the ignition off and then restart the engine, the computer reads the voltage and sets whatever voltage it sees as the minimum TPS voltage for the TPS sensor, even if that voltage is more than 1.1 volt.

The first place to look is for a bad TPS signal ground, broken signal ground wire, or bad connection in the TPS wiring. The TPS connector plug and the 10 pin connector are the two most likely culprits.

The other thing to consider is a bad TPS sensor. Again, dumping the computer codes is a must do item on your troubleshooting checklist. See http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/ or "Surging Idle Checklist
My idle is good. It's the hesitation/surge while driving 40 mph or less that's bothering me. I had a similar problem on my 03 cobra. Swapping plugs fixed that.
 

jrichker

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My idle is good. It's the hesitation/surge while driving 40 mph or less that's bothering me. I had a similar problem on my 03 cobra. Swapping plugs fixed that.
There are two kinds of people here on Stangnet: parts swappers and diagnostic technicians.
The part swappers get poor, tired, and frustrated and have limited success.
The diagnostic technicians test, observe and then diagnose : that's TOD! Their success rate for solid fixes is much higher.
Which group do you want to belong to?
 
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91GTstroked

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There are two kinds of people here on Stangnet: parts swappers and diagnostic technicians.
The part swappers get poor, tired, and frustrated and have limited success.
The diagnostic technicians test, observe and then diagnose : that's TOD! Their success rate for solid fixes is much higher.
Which group do you want to belong to?
I don't want to be a part swapper! Seems to be what I'm doing lately.

So I've done a few things on the checklist. But not all in order.

Should I just start from the top? I even cleaned and swapped out the injector harness.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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It may not be the same day to day, doesn't matter, the computer reads the setting every time you turn the key on.
The one thing nobody does with the tps is check the sweep, make sure the reading is smooth, slowly open the throttle and watch the meter,
 
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91GTstroked

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It may not be the same day to day, doesn't matter, the computer reads the setting every time you turn the key on.
The one thing nobody does with the tps is check the sweep, make sure the reading is smooth, slowly open the throttle and watch the meter,
Yup I did that a few times. It looked pretty smooth. But mine maxed out at 3.95 volts. Is that okay?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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Ok, so:
A you don't want to do the checklist?
B you are a parts swapper but don't want to admit it?
C all of the above?
these questions are based on your last post.
 

91GTstroked

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Jun 14, 2007
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Ok, so:
A you don't want to do the checklist?
B you are a parts swapper but don't want to admit it?
C all of the above?
these questions are based on your last post.
How is running a balance test a parts swapper? Because I said maybe it's an injector problem? I'm not just going to replace injectors.
 

txstang84

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I'm having a similar issue with my '86 Capri; just off idle solid miss-sounds like a rowdy cam, but it smooths out once you get around 1800 ish RPM and revs up cleanly past that...working my way through the checklist over the past few days. I did the EFI swap on my 84 GT about 15 years ago from junked parts and never had any issues-now this bs lol

Good luck man!
 
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