Idling and Starting Problems

Stall problems

Kieth, I found on my 87 5.0 that the Idle Control Motor mounted on the side of the intake was not closing because of carbon buildup. They go for about 60 bucks or so but you can take it apart and clean it, It will work for a while but not as good as a new one. The time spent cleaning it will either fix or eleminate the problem,

No Crank checklist for 5.0 Mustangs

Revised 05-Oct-2010 to update Fluke references.

No crank. slow crank and stuck starter solenoid problems have the same root causes – low battery voltage and poor connections. For that reason, they are grouped together.
Use the same initial group of tests to find the root cause of both no crank and stuck solenoid problems.

Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…

1.) Will the car start if it is jumped? Then clean battery terminals and check battery for low charge and dead cells. A good battery will measure 12-13 volts at full charge with the ignition switch in the Run position but without the engine running.
A voltmeter placed across the battery terminals should show a minimum of 9.5-10 volts when the ignition switch is turned to the Start position and the starter engages or tries to engage. Less than this will result in a clicking solenoid, or slow cranking (if it cranks at all) or a starter solenoid that sticks and welds the contacts together.

Most auto parts stores will check your battery for free. It does not have to be installed in the car to have it checked; you can carry it with you to the auto parts store.

The battery posts and inside of the battery post terminals should be scraped clean with a knife or battery post cleaner tool. This little trick will fix a surprising number of no start problems.

The clamp on with 2 bolts battery terminal ends are a know problem causer. Any place you see green on a copper wire is corrosion. Corrosion gets in the clamped joint and works its way up the wire under the insulation. Corroded connections do not conduct electricity well. Avoid them like the plague...

If the starter solenoid welds the contacts, then the starter will attempt to run anytime there is power in the battery. The cables and solenoid will get very hot, and may even start smoking. The temporary fix for a welded starter solenoid is to disconnect the battery and smack the back of the solenoid housing a sharp blow with a hammer. This may cause the contacts to unstuck and work normally for a while.

A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection while trying to start the car: more than .5 volts across a connection indicates a problem.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .



2.) Check the battery to engine block ground down near the oil filter, and the ground behind the engine to the firewall. All grounds should be clean and shiny. Use some sandpaper to clean them up.

3.) Jump the big terminals on the starter solenoid next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

The rest of the tech note only concerns no crank problems. If your problem was a stuck solenoid, go back to step 1.

4.) Then pull the small push on connector (small red/blue wire) off the starter solenoid (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it cranks, the relay is good and your problem is in the rest of the circuit.

5.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then you have wiring problems.

Typical start circuit...
Diagram courtesy of Tmoss & Stang&2birds



6.) Pull the starter and take it to AutoZone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.


Starter solenoid wiring for 86-91 Mustang



Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.


Electrical checks for the switches and starter solenoid

Remove the small red/blue wire from the starter solenoid. Use a screwdriver to bridge the connection from the battery positive connection on the starter solenoid to the small screw where the red/blue wire was connected. The starter should crank the engine. If it does not, the starter solenoid is defective.

If the starter does crank the engine, the problem is in the clutch safety circuit (5 speed) or Neutral Sense Switch (auto trans) or ignition switch.


Typical start circuit...
Diagram courtesy of Tmoss & Stang&2birds


You will need a voltmeter or test lamp for the rest of the checks. Connect one lead of the voltmeter or test lamp to ground. The other lead will connect to the item under test.
Look for 12 volts on the white/pink wire when the ignition switch is turned to the Start position. Check the ignition switch first.
No 12 volts, replace the ignition switch.

The next step will require you to push the clutch pedal to the floor (5 speed) or put the transmission in neutral (auto trans) while the ignition switch is turned to the Start position.
Good 12 volts, check the clutch safety switch (5 speed) or Neutral Sense Switch (auto trans) for good 12 volts on both sides of the switches. No 12 volts on both sides of the switch and the switches are defective or out of adjustment. Check the wiring for bad connections while you are at it.





See the "Surging Idle Checklist for help with all your idle/stall problems.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

Mine does the same thing, when I start it cold it idles a little bit higher and idles fine, but when its warm I can start it and it dies imediatly unless I rev it and when it does idle in park of neutral its a up and down idle, and I can hear the IAC valve opening and it letting air in to idle up, the IAC is brand new.

I think my problem is the base idle setting, which may be your issue too.

dont wanna steal the spotlight, but mine does around the same but cold or warm my car would start and rise to 1000 rpms then just die. i would restart it but having to give it gas.. now once in a while the car would idle great and then out of no where is would wanna turn off.... i adjusted the idle so it revs at 15-18k rpms and it STILL wants to turn off and i have to rev up... is this what your car is doing? i still haven't figured out the problem due to the fact i dont have time to try things.. but this weekend would be just for the car

I dont know if this will help either of you but today I set my base idle and it solved my problem for the most part. It idles around 750-800 rpm now but no more bouncing idle or having to give it gas to crank it. but it has the dreaded BBK TB whistle now at idle. I reset the computer by unhooking the battery for 15 min and let it idle for a good 20 min.

I'm going to say the major things that attribute to bad idle are vacuum leaks and bad IAC, I dont know about MAF cars because mine is speed density. Just keep looking for vacuum leaks mine had them everywhere, that cause a rough idle and starting problems, but mostly a high idle.

You guys with idle problems could same 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 you idle problems without spending a lot of time and money. 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. :

haha I know but its too hard to read all that stuff..... I have to read technical orders all day long so when I work on my car I do exactly opposite of what I do on jets, I dont read anything and I have no tool accountability whatsoever. Atleast with my car if I loose a screw or a tool its not going to crash in mid flight

strattoc said:

haha I know but its too hard to read all that stuff..... I have to read technical orders all day long so when I work on my car I do exactly opposite of what I do on jets, I dont read anything and I have no tool accountability whatsoever. Atleast with my car if I loose a screw or a tool its not going to crash in mid flight

Click to expand...

I spent 8 years in the Air Force and 3 years in general aviation as an aviation mechanic. Of that time, 8 years of it was as a FAA licensed Airframe & Powerplant Mechanic. It did teach me some discipline about my working habits and the value of good technical documentation. Throwing parts at a problem and jumping around without a troubleshooting plan is counterproductive to getting it fixed correctly without wasting time and money. The the "Surging Idle Checklist , like all the tech docs I post, is designed to save time, money and sweat.

Yeah I agree. I've only been in for a year and a half, I work aerospace propulsion. And we use troubleshooting trees similar to what you have devised that way you dont replace something unless its necessary.

Post the rest of the codes you got. There may be some clues in them.

Code 18 - SPOUT out or wiring fault - look for short to ground in the SPOUT wiring going
back to the computer. Possible bad TFI.

This code can disable spark advance and reduce power and fuel economy.

Remove the passenger side kick panel and disconnect the computer connector.
There is a 10 MM bolt that holds it in place. Disconnect the TFI module connector
from the TFI and the measure the resistance between the yellow/lt green wire and ground.
You should see greater than 100 K (100000) ohms.
Next measure the resistance between the yellow/lt green wire on the TFI module connector and
Pin 36 on the computer connector. With the SPOUT plug in place, you should see less than 2 ohms.

The following is a view from the computer side of the computer connector.


Diagram courtesy of Tmoss & Stang&2birds