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Maintenance, Troubleshooting and Diagnosis Need help? Having troubles with your GT? Need some maintenance tips? Ask your questions here.

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Old 05-08-2007, 12:19 PM   #1
gerzen
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Default 91 code, rough idle

hi fellas, recently i installed a 65 mm explorer throttle body in my 91 stang, y install a 65 mm egr spacer too, and open the intake at 65 mm too to match the all combo, well i use the explorer tps cuting and soldered the wires whit my stang conector, and calibrated the tps but i cant get the .99 volts in the green wire, because the adjust of the tps only let me adjust at 1.04 volts and reset the ECU disconected the battery for a 1 hour, also i have to keep the old explorer gaskets i dont know if i have a leak in there, well so i star the engine and the idle its so rough, and the engine fells whit less power, i run the KOEO and the KOER, and i have in the KOEO the 91 code, in the continuos memory codes, and in the KOER the 91 too, the car still have the rough idle, what the 91 code means? can also have a fuel pump problem? or its the bad gaskets?

thanks in advance
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GT 1991 convertible AOD, GT40p heads, explorer intake, long tube headers, 65 mm TB, 70 mm maf, MSD 6A, K&N filter, FlowMaster 40 Series Delta flow, 130 amp 3G alt., msd wires, 3.73 rear end, mega bite jr. lower control arms, R-17
http://www.supercalle.com/attachment...6&d=1173984067
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Old 05-08-2007, 09:54 PM   #2
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Since you have a 5-speed, Code 91 is EGO or HUGO low output voltage. This code is about the oxygen sensor signal.

Did install that sensor (ACT?) on the new intake?

After you disconnected then reconnected the battery, did you set the idle speed? This is often overlooked.

The computer needs to learn where the new throttle position is.

Disconnect the ISC connector.

Start the engine.

You may need to turn up the idle speed screw to keep the engine running.

While the engine is running, turn on the things that draw big power such as the headlights and A/C.

The computer will be re-learning where the mechanical setting is for the throttle plate.

Allow the engine to run about 2-minutes.

Turn the engine off and reconnect the ISC.

Restart the engine and see if it idles like it should.

The ISC plays a big part of the cold idle circuit during the start up of the engine. The computer has to know where the throttle plate is to help deliver the air fuel mixture.

Keep us posted.
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Old 05-09-2007, 11:10 AM   #3
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thanks Cris, i only change the Throttle body and egr spacer, i didnt change the intake yet, i have a AOD i notice the 91 code means a something problem whit the first selenoid in the EAOD, so like you said i dont have the problem there, maybe its a lean condition, and i didnt do that thing to set the idle screw, thanks for the help just one more question, maybe ist a stupid question but you guys know more than i of this things, where its the ISC? what it is?
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GT 1991 convertible AOD, GT40p heads, explorer intake, long tube headers, 65 mm TB, 70 mm maf, MSD 6A, K&N filter, FlowMaster 40 Series Delta flow, 130 amp 3G alt., msd wires, 3.73 rear end, mega bite jr. lower control arms, R-17
http://www.supercalle.com/attachment...6&d=1173984067
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Old 05-09-2007, 12:38 PM   #4
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Quote:
Originally Posted by gerzen
......where its the ISC? what it is?

The "ISC" solenoid is that thing on the front of the throttle body that looks like a can and has an electrical connector on it.


The newly installed throttle body has to make the computer aware of where the throttle's postion is and help set the idle speed too.

The idle setting procedure mentioned should help with this.

Also be sure that you don't have any vacuum leaks around the new part you've installed.
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Old 05-09-2007, 01:01 PM   #5
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oh yeah i know where it is, its that one in the photo rigth?, im going to do the idle set up, by the way, at how many RPM should be the idle speed? in neutral?
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File Type: jpg DSC01111b.JPG (144.7 KB, 16 views)
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GT 1991 convertible AOD, GT40p heads, explorer intake, long tube headers, 65 mm TB, 70 mm maf, MSD 6A, K&N filter, FlowMaster 40 Series Delta flow, 130 amp 3G alt., msd wires, 3.73 rear end, mega bite jr. lower control arms, R-17
http://www.supercalle.com/attachment...6&d=1173984067
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Old 05-09-2007, 08:08 PM   #6
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The 91 in the Memory means the O2 sensor is not switching
Engine Running, it means it's always reading lean (bank 1 IIRC)

This could very easily be an air intake leak, vac leak, or a gunked up MAF sensor
Any/all could also give you a rough idle
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Old 05-10-2007, 11:30 AM   #7
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yeah meybe its a vacum or air leak because i have to re-use the old explorer TB gaskets, im going to spray a throttle body cleaner or carbu clean at the gaskets and see if the idle change, its so maybe i have an air leak, im going to set the idle too using the method explined by Chris, im going to do that this afternoon i hope resolve the problem
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http://www.supercalle.com/attachment...6&d=1173984067
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Old 05-14-2007, 11:20 AM   #8
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well this weekend i finally fix mi stang, it was a leaky gasket the egr intake spacer one, so i replace, adjust the idle speed whit the IAB disconected, reset the ECU and conected the ECU whit the new idle speed, mi idle now its very smoth, so i run the KOEO and the KOER again, and that was the results:

KOEO all correct i receive the 11 code
memory continus codes again all correct
KOER i receive the 91 code again ,
i make the cilinder balance test, that when the KOER ends you breafly depress the throttle WOT, and the ECU send the results of the cilinder balance, i got the 9 code??? yes only one digit i know because it send me two times nine blinks a large pause an another nine blinks i know its a 99 code because the ECU send all codes twice im rigth? what that means a 9 in the engine cilinder balance???
why im still have the 91 code? if and stop de intake leak?
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GT 1991 convertible AOD, GT40p heads, explorer intake, long tube headers, 65 mm TB, 70 mm maf, MSD 6A, K&N filter, FlowMaster 40 Series Delta flow, 130 amp 3G alt., msd wires, 3.73 rear end, mega bite jr. lower control arms, R-17
http://www.supercalle.com/attachment...6&d=1173984067
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Old 05-14-2007, 12:15 PM   #9
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Did you unhook the battery and let the computer reset?
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Old 05-14-2007, 01:16 PM   #10
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Mmmm.. yes how did you reset the ECU?

A "90" (nine zero) code in the cyl bal test is a "pass"
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Old 05-14-2007, 01:21 PM   #11
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thanks ok so mi cylinder balance its fine, yeah i reset the ECU by disconected the batery for at least 1 hour, then a run again the KOEO and the KOER and i receive the 91 code again
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Old 05-14-2007, 02:08 PM   #12
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Unfortunately, it could be a lot of things

If the Mass Air sensor is clean, and there is no un-metered air getting into the intake (cracks/holes) I'd focus on the O2 sensor circuit next

An open, short to ground, or just worn/bad wiring can throw that code

Also, an old (high mileage) or skunked (otherwise gunked up) O2 can make the ECU think it's reading lean (low voltage)

Check the connection/wiring
If the O2 has over 60K or Mileage Unknown, I'd consider replacing it (them, actually)
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Rear speaker grill-less and butchered for 6x9s
With Accessory Reserve Load springs
Accessory Reserve Load Springs...Whooo Hooo!
The Last Four Eye
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Old 05-14-2007, 03:40 PM   #13
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ok i clean the MAF sensor, so thats fine, how i can chek the O2 sensors? can i just remove clean it? its a way to know the shape of the O2 sensors? i mean any volts readers at the O2 sensors?
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Old 05-14-2007, 05:25 PM   #14
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Yes, there's ways to test it
It's a little tricky though


Testing A HEGO (Heated Exhaust Gas Oxygen sensor)

First off, look at the HEGO connector-the side connected to the HEGO

If you put the big clip on the left, there should be four actual connection spots (sometimes three)

X = connection

X l X
X l O
=
Pwr Grnd l HEGO Sig
Key Pwr l Sig Ret/HEGO Grd (not on all)

Test 1 HEGO Heater Element

Key off, disconnect HEGO
Connect DMM between Key Pwr and Pwr Grnd

if reads 2 - 5 ohms at room temp, HEGO Heater Element is faulty

Test 2 Key Power

Key off, disconnect HEGO
Connect DMM between Key Pwr and Pwr Grnd ON VEHICLE/MAIN HARNESS SIDE OF CONNECTOR (all other tests are on the sensor side)
Key on
Reading of 10.5 volts or higher = wiring/harness/ground problems


Test 3 HEGO Sig

Key Off, disconnect HEGO
Connect DMM between HEGO Sig and Neg Bat. terminal
Run engine for 2 min. @ 2K RPM

if reads 0.5 volts or higher, HEGO may be faulty

Test 4 HEGO Response (to exhaust)Key Off, disconnect HEGO
Connect DMM between HEGO Sig and Neg Bat. terminal
Run engine for 2 min. @ 2K RPM

Create vac leak (disconnect vac hose to intake manifold)

If voltage drops and fluctuates, HEGO may be faulty
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Rear speaker grill-less and butchered for 6x9s
With Accessory Reserve Load springs
Accessory Reserve Load Springs...Whooo Hooo!
The Last Four Eye
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Old 05-15-2007, 11:40 AM   #15
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hey men thats a great info, im going to do the test the way that you say, whit that im going to be sure by the real condition of the HEGO sensor´s, thanks a lot again oh a last question the 91 code describe a lean condition in the right side, which one its the rigth side? the pilot side or copilot? im asking that because the engine can see from two wiews, by the front of the vehicule or from the rear side, i think the most logic thing its to take the pilot side as the right side, im correct?
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http://www.supercalle.com/attachment...6&d=1173984067
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