High idle gremlin?

[txblackmach1]

been having a high idle problem with mustang. at first sounded like a big vacuum leak but after doing the basic checks i couldn't find one. so this is the break down of the setup and what i have done.
So this is my setup
88 mustang with a 95 cobra engine. (I purchased a running 95 cobra for suspension and ended up using the engine as well.)
I did swap out a mystery cam it had with a tfs1.
I did the mass air swap using a9p.(I converted car from aod to t5)

Now before the engine swap the car was running normal. I did notice was that from time to time it would rev up by itself when I would depress the clutch when I was in parking. It only did it a handful of times. And the other was that after I would drive it for a while it wouldn’t want to crank over anymore.. I would to have to wait till it cooled down. (Possible a bad tfi module)

Initially I was just going to put the gt40 heads/rockers/ trick flow intake and put it in my block but since the cobra was running and idling fine when I removed it I decided to save some time and do the swap. Since my oem engine was extremely dirty from previous owner not changing gaskets. I prepped the cobra engine to fit my fox setup. Pretty much changed out the timing chain housing/balancer to fox version. I also intake was removed to see the condition of valley. So brand new gaskets where installed when I put engine in car. 24lb injectors/matching c/l

Finally I can get to the problem.
When I turn on the car the car will rev up to 2000 rpm and within a couple of seconds it will gradually climb up to 2800rpm. And within a minute or 2 the header are cherry red hot. Now I tried several things while trying to trouble shoot it.

• Tps. I tried to adjust tps but I only had a range of .53-.64 on signal wire (green) 4.95 volts on orange wire and I was using black wire for my ground. I swapped it with another spare tps and it gave me same numbers. At that point I went to store and bought a brand new one. And that one gave me same numbers as well.. which came to conclusion that tps was fine. I also checked the 5 volt reference on the sensors that are in line and they all checked out. I even checked the tps signal wire at the computer and still got .64 volts koeo.
• Iac has been cleaned out/while engine is on and revved up it has no change on idle.
• Mass air meter. While revved up I can disconnect mass air meter and car will idle down to about 800-950 and when I rev it up it take a long time to idle back down.
• Timing. All this time the car was set to 10-11 degrees of timing. Now with everything connected as it should I went ahead and retarded timing because I notice that when I would it would idle down. I was able to get it to idle at 800 rpm but the timing was at -12 (balancer goes up to -10 and it was a bit after that). The down side is that the header still seem to be getting red hot and when I rev it up it’s not very responsive.
• I swapped computer to an a9L and had same results
• I cleaned out salt and pepper shakers and same results
• I swapped out the main harness/injectors harness from 92 gt with factory mass air and still had same results.
• Remember I mentioned about mystery cam.. well since I didn’t know what cam was in cobra engine or how it was installed that’s when I opened it up and swap that mystery came with tfs1 that I had. While in process I swapped out to different intake and same results.
• And before most of those things where swapped out the sprayed car with brake cleaner to see if I can find a vacuum leak and I didn’t have any luck. I even went as far as plugging up all the vacuum ports but had same results.
• I even swapped out intakes with new gaskets with same results.
• swaped out to another 24lb maf same results (i even went back to 19lbs injectors/ stock maf with same results)

The one thing I haven’t changed is o2 sensors. I didn’t bother to changed them since I didn’t have issues before
I know this was very long but I wanted to put everything out there since I have been fighting this issue for the past 4 week on and off when I have a chance after work.
any advice things that i have done or not done will be greatly appreciated.

 

[90sickfox]

When you swapped from auto to 5 speed did you do anything with the o2 sensor harness. Theres a jumper that needs to be moved. With the clutch are you using the clutch switch ? On an automatic there is a jumper on the connector....for 5 speed the jumper is pulled out and the connector plugged in.

Cherry red headers means the car is going lean. If you unplug the idle air control valve does the idle decrease ?

How did you get the 92 main harness to work on the 88 ? The main computer harnesses are not compatible due to connectors on drivers side by strut tower.

The timing shouldn't be retarded. It should be somewhere between 10° and 14° with the spout unplugged.

How did you do the mass air conversion ?

 

[txblackmach1]

1. i didn't do anything with with 02 harness. as far as the connector part i remember doing something down there when i added the pedals. i will have to double check this to cross this out of the list (when i did conversion everything was working good after about 3 weeks is when i did the engine swap and its when i started having the issues)
2. if i uplug the iac nothing happens. i tried 2 different iac with same outcome. the only way i can get it to rev down is my disconnecting the mass air.
3. that is a spare harness i bought in swap meet. guy sold it as 92 but it does have the 2 connectors on the drivers side so it must be 90-91 mass air harness.
4. yes i under stand the timing should be stock at 10º. which is where its at right now. but for the sake of troubleshooting i ended up retarting it to see what if anything would change. but like i said i have put it back to 10-12º.
5. when i originally did the conversion i ran my mass air plug wires to the inside and following lmr instructions on swapping the pins. off the top of my head dont remember what pins i swapped. but like i mentioned earlier when conversion was done the car was not having this high idle issue. issue came when i decided to swap out the engine. keep in mind that this engine came from a running car i made sure of that. the only thing i did was change out the intake gaskets to make sure everything look good in the valley. that being said 1st thing that comes to mind is the intake gaskets where not properly installed or damaged. well when i swamped intakes i put new ones. fel-1262s. is it a possible that i installed twice in a row.. maybe but just for reference i have done 25+ hci swaps and never had and issue with bad seal on the intake. at the end of day i am human so something went wrong and that what im trying to find out.

 

[90sickfox]

Ok...so you're not completely new to this.

The o2 sensor harness is on the passenger side of the frame rail. Somewhere in the neighborhood of the carbon canister location. Unplug it and start it up. I had a weird issue with idle once. Found out the o2 sensor harness was grounding out at the k member. If you unplug and have same issues then you can check that box off.

Can you hook up a vacuum gauge to an intake port and post a video of it running ? They are cheap and one of the best diag tools out there.

 

[General karthief]

No where in the thread did I see any mention of you checking for computer codes. And don't say there are no codes, there should be an 11 code that means it checked out, if you get no codes or the computer does not communicate you have a computer/wiring problem.

 

[txblackmach1]

90sick fox- i did disconnected and it didn't make no difference.
general- wow.. your right i failed to put that on there.. thats definitly good info
so when i ran the codes i got
31-evp low volatge (all i did here was verify that i was getting 5 volts on the signal wire on tps) or what is the correct way to verify trouble shoot this?
67-clutch not depressed (this is what sickfox was talking about i think)
the rest i didnt put much thought since i deleted all egr stuff.. i have block of plate and all vaccume lines have been removed.
81
82
85
84

 

[General karthief]

The surging idle checklist has the procedure for checking the tps and base idle reset, some adjustments require a computer reset

 

[txblackmach1]

thats one of my issues i can get my tps to read more than .64 volts..
i have tried couple used ones and currently have a brand new one with same results.
i even borrowed one from my friend. before i took it off his car his was set at .98. when i swapped it to mine read .64 .
this is a stock throttle body so hasn't be modded in any way. what i did do is filed off one of the old ones and adjusted to be .95 on my multi-meter. but unfortunately the results where the same the car still had the high idle..

i have been so busy with work that i can only work on the weekends.. i will continue to trouble shoot this weekend and see if i come up with some different results.
i have a feeling that its probably something small that either i missed because im so frustrated or broke because its 30+ years old.

either way i really appreciate you guys input..

 

[General karthief]

Make sure the adjustment screw on the throttle body is not holding the blade open.

 

[90sickfox]

The EVP is for the egr sensor. Its saying it's not in the correct position. It should be 5 volt reference. On the fox it's the white plastic thing sitting on top of the valve.( not sure on cobra engine ) You can check the egr with a vacuum pump. With the egr unbolted it should open the pintle with vacuum applied. There's also a vacuum solenoid that the egr vacuum line runs to. This sensor works just about the same as the tps. The voltage reference is 5 volts and the signal wire should increase voltage as the pintle opens. The other wire is ground.

If the computer thinks the egr isn't working properly it should ignore the egr system. I dont think I've ever seen an egr cause a high idle. If the vacuum line is run straight to it at idle it would open the valve and allow exhaust gas into the chambers. That could possibly affect idle but usually causes a low rough idle. I don't know what the computer would do to try and compensate for that.

 

[txblackmach1]

GENERAL- thats one of the 1st thing i checked.. right now the screw is hair from touching it. i even disconnected the throttle cable thinking that maybe is was causing an issue.
SICKFOX-well i eliminated the whole egr system and i agree i have never heard of that causing an issue..

 

[jrichker]

GENERAL- thats one of the 1st thing i checked.. right now the screw is hair from touching it. i even disconnected the throttle cable thinking that maybe is was causing an issue.
SICKFOX-well i eliminated the whole egr system and i agree i have never heard of that causing an issue..

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

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 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


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.

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.

 

[txblackmach1]

UPDATE- high idle issue fixed..IAC valve stuck open. thats one of the first things i clean.. but since it was working before i didn't think to check it again. i replace it with new one and my idle is back to normal. i do have a slight surge but its normal. the car is not stock and i work with the slight surging issues. how do you know if its stuck open? high idle is the obvious one but you will also here that its sucking in alot of air through throttle body. like a vacuum. and just to confirm i turned car on with air tube disconnected and put my finger on the iac port on the inside of throttle body. car created suction and car turned off.

another thing i did was go back to my original wiring harness but i deleted the salt and pepper connections and soldered the wires. having the computer disconnected for couple of hours i imagine helped reset the system.

it was a dreadful couple of weeks trouble shooting this only on my spare time. but glad its over.. thanks for all the help and information shared. at least if someone has a similar issue this will pop up in the search and help them out.

eddie