1993 Mustang Cobra TPS Issue

98 svt

Well-Known Member
Established Member
Premium Member
Joined
May 16, 2005
Messages
23,960
Location
Massachoooosetts
Go to the local parts store and grab a new tps. They are under $50. If it doesnt fix the issue, return it.
Certainly sounds like it's the culprit.
 
Last edited:

RunninHorse

Active Member
Established Member
Joined
Feb 15, 2020
Messages
112
Location
San Antonio, Texas
If it isnt the TPS, then what else could it be?
An EEC failure can also cause constant 5vdc at the green TPS wire, but you'd have more than just a surging idle.

Have there been any recent changes to the car? When did the surging idle start?

It's worth running KOEO/KOER self tests. Even if the check engine light isn't on. See attachment.

In general, a base idle reset should help with surging idle. See attachment. I'd run codes first though.

Any tuner worth his salt should tell you not to try to tune it while there are any type of issues. Get everything fixed and all codes cleared first.
 

Attachments

  • DIY KOEO_KOER_CylinderBalance.pdf
    1.9 MB · Views: 168
  • Base Idle Reset.pdf
    255.1 KB · Views: 157

Tbrake1978

Member
Established Member
Joined
Mar 6, 2020
Messages
38
Location
Kansas
An EEC failure can also cause constant 5vdc at the green TPS wire, but you'd have more than just a surging idle.

Have there been any recent changes to the car? When did the surging idle start?

It's worth running KOEO/KOER self tests. Even if the check engine light isn't on. See attachment.

In general, a base idle reset should help with surging idle. See attachment. I'd run codes first though.

Any tuner worth his salt should tell you not to try to tune it while there are any type of issues. Get everything fixed and all codes cleared first.
Thanks for the info.
No changes
Its idle surged ever since the first day I got the car. I backed the timing to 10-11 degrees but that is the only adjustments I have recently made.
 

Tbrake1978

Member
Established Member
Joined
Mar 6, 2020
Messages
38
Location
Kansas
Update:

Replaced TPS- Was able to get my .98V reading

Changed to a X3Z computer.
Performed Base Idle reset
Idle still surges a little bit
1/4 Throttle seems like full throttle and doesnt return to idle right away
 

RunninHorse

Active Member
Established Member
Joined
Feb 15, 2020
Messages
112
Location
San Antonio, Texas
Update:

Replaced TPS- Was able to get my .98V reading

Changed to a X3Z computer.
Performed Base Idle reset
Idle still surges a little bit
1/4 Throttle seems like full throttle and doesnt return to idle right away

If you have .98 vdc at closed throttle, your computer should register WOT at 3.69 vdc. (Closed throttle voltage plus 2.71). You could monitor the voltage as you open the throttle to see how soon you get there.

I spent a little time tuning the X3Z in my coupe. I'm no expert, but I do remember there is something that controls how quickly it returns to idle. @decipha would be the best person to help you figure that out over at EFIDynoTuning.com.

I loaded one of his base tunes on mine and my coupe ran much better. It was a night and day difference for me. Still kills me that I never got it back to the track after the initial tune changes.

I used a QuarterHorse by Moates. 'QuarterHorse' for Fords [QH1] - $249.00 : Moates.Net
 

Tbrake1978

Member
Established Member
Joined
Mar 6, 2020
Messages
38
Location
Kansas
If you have .98 vdc at closed throttle, your computer should register WOT at 3.69 vdc. (Closed throttle voltage plus 2.71). You could monitor the voltage as you open the throttle to see how soon you get there.

I spent a little time tuning the X3Z in my coupe. I'm no expert, but I do remember there is something that controls how quickly it returns to idle. @decipha would be the best person to help you figure that out over at EFIDynoTuning.com.

I loaded one of his base tunes on mine and my coupe ran much better. It was a night and day difference for me. Still kills me that I never got it back to the track after the initial tune changes.

I used a QuarterHorse by Moates. 'QuarterHorse' for Fords [QH1] - $249.00 : Moates.Net


I bought an SCT Eliminator Chip and have a tune scheduled for this Thursday. The shop is supposed to be the best in the area. I am just hoping I can get it there and them figure it out
 

MG0h3

Well-Known Member
Established Member
Joined
Jul 23, 2014
Messages
13,683
Location
El Paso, TX
Man Ive been away from foxes ive forgotten a lot.

So do you get a steady idle at the correct RPM and it surges once the IAC is plugged back in?


Sent from my iPhone using svtperformance.com
 

Tbrake1978

Member
Established Member
Joined
Mar 6, 2020
Messages
38
Location
Kansas
Man Ive been away from foxes ive forgotten a lot.

So do you get a steady idle at the correct RPM and it surges once the IAC is plugged back in?


Sent from my iPhone using svtperformance.com

It usually surges for about a minute and then it will idle ok and then randomly starts to surge again
 

Tbrake1978

Member
Established Member
Joined
Mar 6, 2020
Messages
38
Location
Kansas
Once I put the X3Z computer in, set base idle, it runs really good now. Keep fingers crossed. I drive it 45 miles to Tune Shop... I will keep this post updated on how everything goes.
 

Users who are viewing this thread



Top