• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

Engine 1987 LX 5.0 5 Speed - idle and . . .

  • Thread starter Thread starter nathan_erie
  • Start date Start date Dec 31, 2018
  • Tags Tags
    hanging rpm idle idle issues
N

nathan_erie

New Member
Dec 31, 2018
1
0
1
Cumming, Georgia
Dec 31, 2018
#1
  • Dec 31, 2018
  • #1
Hello all. This is my first post on this forum. I thank you in advance for the time and consideration you give to my issue. So, I just picked up a 1987 Ford Mustang LX 5.0, hatchback, 5 speed, all original, 100% stock, 27k miles. The thing looks like it was buried in an air tight time capsule for the last 30 years. Unbelievable condition. Here is my question - the car runs great, starts fine, but does have a tendency to "hunt" a little bit for idle. The issue is intermittent. Sometimes the car will idle at around 1700 RPM and other times it idles around 800 RPM. The other thing it does which is extremely annoying is . . . sometimes when you are shifting up, when you push in the clutch and take your foot off the gas, the RPM's will increase. I love the fox body mustang it was on my bucket list to own one, but I'm not sure if this is normal behavior for these cars or what. So far, I've replaced the IAC, adjusted the TPS to 0.93 (it shows 4.7 @ WOT), and OBD1 shows no issues, it's a clear scan. If you were in my shoes (I'm not a gearhead - I can wrench on my two stroke dirt bike but cars are out of my league), what would you do? Thank you very much for your time and consideration to my post. I can post photos if anyone is interested.
 

General karthief

wonder how much it would cost to ship you a pair
20+ Year Stangneter
Aug 25, 2016
27,926
10,572
203
polk county florida
Dec 31, 2018
#2
  • Dec 31, 2018
  • #2
On the main tech page there is a technical/how to thread, in there you will find the surging idle checklist, go through the list step by step and it will resolve most all idle/stall issues. It shows you what to look for when checking for codes too. Thanks to jrichker it has solved many a mustang owners problems, even makes me look like a hero when talking to others about their stangs, and post some pics of the stang you have too, we are kinda picture whores around here, no pics, didn't happen!
And welcome to stangnet!
 
J

junkyardwarrior

Well-Known Member
Jan 10, 2011
400
113
63
Jan 1, 2019
#3
  • Jan 1, 2019
  • #3
Check the sweep on the TPS with an analog volt meter. You can also do it with a digital, but it's easier to see a dead spot with an analog meter.

Then check for vacuum leaks. These things are SUPER sensitive to vacuum leaks, so even a little bitty one can cause the surge. Many people never find them and just get tired of chasing their tail.
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
43,259
17,943
224
Massachusetts
Jan 1, 2019
#4
  • Jan 1, 2019
  • #4
Given the low mileage, I assume this car sits more than drives. How is it stored? Battery disconnected? Or on a trickle charger?

Often times cars that have the battery disconnected don't regain idle control for some time...over s period of starts. Of course if car gets stored and battery disconnected, it starts all over again.

Have you actually performed the idle reset procedure?
 

jrichker

StangNet's favorite TOOL
In Remembrance. Thank you for your contributions
Mar 10, 2000
27,512
2,813
234
Dublin GA
Jan 2, 2019
#5
  • Jan 2, 2019
  • #5
Drive the car at highway speeds for 15-20 minutes to give the computer a chance to relearn the adaptive settings again. If that doesn't fix it, do the next 2 steps in order that they are listed.

No code 11 (two flashes when the computer dumps the codes)? A perfectly functioning system will always get a code 11, it is the everything is OK code. The 11 code is computer passed its internal self test.
If you don't get an 11, you have computer or wiring problems.
Please check and repost.

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.
 
Reactions: Neuron and General karthief
You must log in or register to reply here.

Similar threads

A
1987 5.0 speed density Foxbody crank no start
  • Alan2204
  • May 23, 2026
  • Fox 5.0 Mustang Tech
Replies
10
Views
309
Fox 5.0 Mustang Tech May 30, 2026
Mcmahst
Fox Fuel Pump Issues After Replacement/Upgrade
  • Ryu
  • Jun 23, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 2
Replies
23
Views
569
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Jul 5, 2026
Ryu
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
H
Hanging idle issues
  • HydraX
  • Mar 22, 2025
  • SVT Tech Forum
Replies
5
Views
604
SVT Tech Forum Aug 4, 2025
squeak93
Engine 1990 LX 5.0L EFI Mustang Fuel Management Problems - HELP!
  • 5.0LXStanger
  • May 25, 2025
  • Fox 5.0 Mustang Tech
  • 2 3
Replies
45
Views
2K
Fox 5.0 Mustang Tech Jul 11, 2025
5.0LXStanger
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 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?