Was Idling Fine.....

f8tlfiveo

My wife likes my spool and blow-off valve.
Aug 8, 2007
1,585
102
64
Lancaster, PA
Just put my engine back together, gt40 heads, tfs1 cam, explorer intake. When I started the car I had it idling great at first around 800-850rpms.. It was like that for at least a half an hour idling in my driveway while I was checking for leaks and making sure everything was right. Now I have a surging idle, not sure how it happened, I didn't change anything. I do have some codes that show up koeo, 31, 67... Forgot to push clutch in, egr valve is there and plugged in, just not attached. I plan on turning that off with my quarterhorse in the tune. Koer, 31,91... I guess that means one 02 sensor is reading lean or is not working correctly. Any ideas?


Sent from my iPhone
 
  • Sponsors(?)


jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,245
2,594
234
74
Dublin GA
lowendmac.com
No guesses here, just a tested and proven way to find your idle stall and surge problems.


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. 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. :D

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 159,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
 

f8tlfiveo

My wife likes my spool and blow-off valve.
Aug 8, 2007
1,585
102
64
Lancaster, PA
Yes I was looking over this earlier, when I have time I want to go down through the list, I was more wondering why it ran fine for a half hour, then decided to start surging.. Could it have anything to do with the keep alive memory being blank from the battery being unplugged.


Sent from my iPhone
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,245
2,594
234
74
Dublin GA
lowendmac.com
Yes I was looking over this earlier, when I have time I want to go down through the list, I was more wondering why it ran fine for a half hour, then decided to start surging.. Could it have anything to do with the keep alive memory being blank from the battery being unplugged.


Sent from my iPhone
It is possible.
If you drive at highway speeds for 15-30 minutes, it will smooth out if that is the problem. If it doesn't smooth out, fix the O2 sensor problem first.

Code 41 or 91. Or 43 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 11-Jan-2015 to add check for fuel pressure out of range

Code 41 is the passenger side sensor, as viewed from the driver's seat.
Code 91 is the driver side sensor, as viewed from the driver's seat.

Code 172 is the passenger side sensor as viewed from the driver's seat.
Code 176 is the driver side sensor, as viewed from the driver's seat.

Code 43 is not side specific according to the Probst Ford Fuel injection book.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors 87-93 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear.

Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor , you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.

Backside view of the computer wiring connector:


87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
The computer pins are 29 (L\RH O2 with a dark green/pink wire) and 43 (LH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer. Using the Low Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
From the Dark Green/Pink wire on the RH Os sensor harness and the Dark Green/Pink wire on the computer pin 29

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 29

94-95 5.0 Mustangs:
Computer pin 29 Red/Black – LH O2 sensor
Computer pin 27 Gray/Lt blue – RH O2 sensor
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 27

There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged and the contacts are clean and not coated with oil.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Check the fuel pressure – the fuel pressure is 37-41 PSI with the vacuum disconnected and the engine idling. Fuel pressure out of range can cause the 41 & 91 codes together. It will not cause a single code, only both codes together.

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

Code 41 can also be due to carbon plugging the driver’s side Thermactor air crossover tube on the back of the engine. The tube fills up with carbon and does not pass air to the driver’s side head ports. This puts an excess amount of air in the passenger side exhaust and can set the code 41. Remove the tube and clean it out so that both sides get good airflow: this may be more difficult than it sounds. You need something like a mini rotor-rooter to do the job because of the curves in the tube. Something like the outer spiral jacket of a flexible push-pull cable may be the thing that does the trick.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
 
Thread starter Similar threads Forum Replies Date
D Idles fine, Rev engine high manually, engine comes down and eventually dies 2.3L (N/A & Turbo) Tech 2
D Idles Fine, Rev engine High Manually, engine comes down and dies. 2.3L (N/A & Turbo) Tech 0
1992 5.Slow GT B303 cam swap on my 92 GT now running rich and falls on its face, idles fine tho. Fox 5.0 Mustang Tech 6
1995COBRA 95 Cobra starts right up and idles fine at first, but then after about 2 minutes, I try and restart and it does not hold an idle. 1994 - 1995 Specific Tech 12
S Engine 95 Gt Fine At Idle Overheats At Speed 1994 - 1995 Specific Tech 4
96nickSn95 Runs Fine But Idles Low When In Drive SN95 4.6L Mustang Tech 7
Johhny J Car Idles Fine Then Dies Fox 5.0 Mustang Tech 1
V8_Kind_Of_Guy Car Idles Fine, Give It Gas And Wants To Die Fox 5.0 Mustang Tech 11
M Idle Drops Immediately After Start, Then Fine 1994 - 1995 Specific Tech 6
B 98 Gt Starts Fine Then Shuts Off While Driving/idling SN95 4.6L Mustang Tech 20
B Engine Engine Starts, Idles Fine But When I Push The Peddle It Dies. SN95 4.6L Mustang Tech 4
PlatinumDevil Car wouldn't idle, clunk, running fine... SN95 4.6L Mustang Tech 0
Crs Car starts, idles fine, dies when put in gear. Classic Mustang Specific Tech 3
D 351 idles fine dies when in gear Classic Mustang Specific Tech 4
Methodical Car idles fine until..... see pics inside...help 1994 - 1995 Specific Tech 20
6 5.0 missing at idle, but runs fine otherwise Fox 5.0 Mustang Tech 1
Pokageek Car idles fine but cuts out half the time at a stop. Ideas? 1994 - 1995 Specific Tech 18
mustanggt94 TWEECER NEWBIE HERE! Need help fine tuning: Idle & Bucking problem 1994 - 1995 Specific Tech 11
L HELP: drives fine for 15 min, then wont rev up or idle nicely SN95 4.6L Mustang Tech 3
SemperFIGOD Idle and IAC Digital Self-tuning Forum 6
J Engine Rough Idle after Timing Chain Replacement - No Codes 2005 - 2014 Specific V6 Tech 0
9 Engine Won’t go past idle Fox 5.0 Mustang Tech 0
mustangpauly 351w swap need help will not idle Digital Self-tuning Forum 8
G 3.8/auto - ZERO codes - terrible idle - not driveable - backfires SN95 V6 Mustang Tech 1
J Engine Help with cold starts and cold idle Fox 5.0 Mustang Tech 7
M Progress Thread 2014 Automatic idle/accelaration Issues 2005 - 2014 S-197 Mustang -General/Talk- 0
7991LXnSHO Drivetrain New hanging idle problem Fox 5.0 Mustang Tech 7
SemperFIGOD Idle kpa Digital Self-tuning Forum 9
C Engine Higher idle then normal 1994 - 1995 Specific Tech 8
A Hunting idle 4.6 2v with stage one cam Digital Self-tuning Forum 0
92j3ieje8 Car turns off and idles low. 1996 - 2004 SN95 Mustang -General/Talk- 0
1 2005 V6 shudder at idle in gear 2005 - 2009 Specific Tech 6
danielhv Bad Idle Air Control Valve? Digital Self-tuning Forum 9
J Idle Adjustment Issues 2.3 Turbo fuel injectedto 2.3L (N/A & Turbo) Tech 16
0 4.6 2v SOHC 2k rpm Idle, help reading engine data SN95 4.6L Mustang Tech 2
I Microsquirt idle after clutch engagement Digital Self-tuning Forum 1
africansnowowl Engine Update: Another rough idle thread Fox 5.0 Mustang Tech 17
J Looking for 2005 GT OBD2 idle sensor reading 2005 - 2014 S-197 Mustang -General/Talk- 2
J Engine New Manifold nightmare idle and stall 2005 - 2009 Specific Tech 4
C 2013 GT low oil pressure at low RPMs or idle 2010 - 2014 Specific Tech 0
R Engine Remove the Idiot from the equation. Idle/hesitation issue. Fox 5.0 Mustang Tech 3
C 2014 Mustang Gt/Cs Idle and dying issue 2010 - 2014 Specific Tech 2
T MS3 AC Idle Up Settings Digital Self-tuning Forum 1
93silverlx50 Engine Car in limp mode, fuel spitting out of tailpipes, missing rough idle Fox 5.0 Mustang Tech 9
markinms Engine Should Auto Trans Be in Drive When Setting Base Idle Fox 5.0 Mustang Tech 7
R Fuel Throttle body idle screw 1994 - 1995 Specific Tech 2
darryl paarman A/C idle up control- Low input or High. ? Digital Self-tuning Forum 2
C Engine Gray smoke from exhaust. Smells like gas. Fox 5.0 Mustang Tech 15
lamrith New MSPnP2 in 94 Mustang, need help getting stable idle once warmed up. Digital Self-tuning Forum 1
J Idle issue still!! Replaced several parts.. looking for more ideas!! Fox 5.0 Mustang Tech 12
Similar threads