• Mustang Forums
  • 1996 - 2004 SN95 Mustang -General/Talk-
  • SN95 4.6L Mustang Tech

04 Gt Rough Idle. Out Of Ideas...

  • Thread starter Thread starter richy28510
  • Start date Start date May 25, 2013

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
May 25, 2013
#1
  • May 25, 2013
  • #1
I recently pusrchased a 04 stang. After a few days it developed a slight rough idle. It has gotten worse and worse, but does not throw a code. I've replaced plugs, air filter, fuel filter, pcv valve, upstream 02 sensors. . I cleaned the throttle body and injectors. I unplugged the maf while it was runnng and idle smoothed out and it ran amazing. So I figured maf was bad got new one installed and same thing. I reset the computer a few times. Nothing is fixing this rough idle any suggestions???
04 ,72k miles.
 

COramprat

...I can take it. I think.
20+ Year Stangneter
Mar 2, 2003
8,474
1,463
223
Sea of Tranquility
May 26, 2013
#2
  • May 26, 2013
  • #2
Check the fuel rail pressure sensor. You can pull the vacuum line off and if it squirts fuel at you, then it is bad.



Look toward the firewall on the drivers side.
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
May 26, 2013
#3
  • May 26, 2013
  • #3
I will check it. Thanks
 

Mattstang04

15 Year Member
Sep 15, 2006
1,152
144
104
St. Louis, MO
May 27, 2013
#4
  • May 27, 2013
  • #4
You may want to check your idle air control valve. When my idle got rough, I replaced it and it took care of the problem. It is a fairly common problem with Mustangs.
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
May 29, 2013
#5
  • May 29, 2013
  • #5
Tnyway to test if it id bad?
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
May 29, 2013
#6
  • May 29, 2013
  • #6
Stupid tablet...Anyway to test it?
 

COramprat

...I can take it. I think.
20+ Year Stangneter
Mar 2, 2003
8,474
1,463
223
Sea of Tranquility
May 29, 2013
#7
  • May 29, 2013
  • #7
I think there is a voltage test. It's in a Chilton's. Go get one...best 25 bucks I ever spent.

Generally with a bad IAC the car will not run without mashing the gas. Keeping the RPM's up will allow it to run but as soon as you let off the car will die. I've never heard of any rough running issues with the IAC but that doesn't mean it doesn't happen.

The Fuel Rail sensor is an easy one. Once you pull the vacuum line you will know it there is a problem.
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
May 31, 2013
#8
  • May 31, 2013
  • #8
Check the fuel rail sensor working properly.
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
May 31, 2013
#9
  • May 31, 2013
  • #9
Hopefully when I get my sct itsx tuner Monday I can map the idle to see whats going on.
 

COramprat

...I can take it. I think.
20+ Year Stangneter
Mar 2, 2003
8,474
1,463
223
Sea of Tranquility
Jun 1, 2013
#10
  • Jun 1, 2013
  • #10
It may tell you something, then it may not. Is it throwing any codes?
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
Jun 1, 2013
#11
  • Jun 1, 2013
  • #11
No codes
 
Reactions: DJ662

COramprat

...I can take it. I think.
20+ Year Stangneter
Mar 2, 2003
8,474
1,463
223
Sea of Tranquility
Jun 2, 2013
#12
  • Jun 2, 2013
  • #12
Might be a vacuum leak. Check all the lines and hoses for cracks.
 

Rusty67

20+ Year Stangneter
Dec 3, 2002
3,749
37
109
LA, CA
Jun 2, 2013
#13
  • Jun 2, 2013
  • #13
If you can have the ECU read for TIDs you might find something useful. My dad's Mustang had issues and I found it was failing TIDs relating to the DPFE but it wasn't throwing codes. I checked and the DPFE hoses were bad and causing a vacuum leak. Car idles great now. Not saying that is your problem.

As far as the IAC is concerned, it wouldn't hurt to yank it out and clean it.

If you are worried about a vacuum leak you can take it to a mechanic and pay for a smoke test.
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
Jun 6, 2013
#14
  • Jun 6, 2013
  • #14
Just installed my tuner and ran it and blam at 80 it broke up and threw a code. Bad coil. But I think I have more issues than that. Will check vacuum lines
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
Jun 6, 2013
#15
  • Jun 6, 2013
  • #15
Found out car sat up for 3 years.
 

Rusty67

20+ Year Stangneter
Dec 3, 2002
3,749
37
109
LA, CA
Jun 6, 2013
#16
  • Jun 6, 2013
  • #16
The TIDs would have told you about a missfire on the cylinder without it throwing a code. You may or may not have a bad coil. Could also be the spark plug or the injector. Move the coil pack to another cylinder and read the TIDs after you have the issue again. You should see the missfire count in the TID follow the coil pack. If not you have another problem.
 

richy28510

New Member
May 25, 2013
12
1
1
Arapahoe, North Carolina
Jun 8, 2013
#17
  • Jun 8, 2013
  • #17
Somehow the coil connector unplugged itself . Replugged and it sounded like it (normal self) ses light went off. I will have the car at the shop tomorrow to test your idea.
 
You must log in or register to reply here.

Similar threads

A
Rough idle - cylinder 1 and 6 misfire HELP
  • austindavies935
  • Jul 24, 2025
  • SN95 4.6L Mustang Tech
Replies
12
Views
732
SN95 4.6L Mustang Tech Jul 24, 2025
gkomo
K
Engine 2000 Mustang GT - Fuel issue post-blown spark plug repair
  • kenster1092
  • Feb 26, 2026
  • SN95 4.6L Mustang Tech
Replies
4
Views
375
SN95 4.6L Mustang Tech Mar 10, 2026
kenster1092
K
0
Engine Multiple o2 sensor codes, car runs terrible
  • 02newedge
  • Jun 12, 2025
  • SN95 4.6L Mustang Tech
Replies
5
Views
536
SN95 4.6L Mustang Tech Jul 19, 2025
squeak93
SURGING IDLE / NO IDLE CHECKLIST FOR 1999–2004 MUSTANG GT (4.6L 2V) - Work In Progress
  • Noobz347
  • Aug 30, 2025
  • 1996 - 2004 SN95 Mustang -General/Talk-
Replies
0
Views
929
1996 - 2004 SN95 Mustang -General/Talk- Aug 30, 2025
Noobz347
8
Engine Rough idle and aggressive sputtering when accelerating
  • 88vertible
  • Aug 13, 2025
  • Fox 5.0 Mustang Tech
Replies
4
Views
1K
Fox 5.0 Mustang Tech Dec 13, 2025
Jarhead67
J
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1996 - 2004 SN95 Mustang -General/Talk-
  • SN95 4.6L Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?