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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 03-04-2014, 09:39 AM   #1
samltheriault
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Vehicle: 89 mustang lx
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Exclamation car idles rough for a bit then runs fine. need help

so over last winter i did an engine bay shave and hid just about as much as possible. over last summer i was working out all the little nicks and crannies but now I'm down to the last one and cant figure it out. when cold the car starts but wont stay running with out feathering the gas for about a min then idles relatively ok then perfect after a little bit. the IAC valve and vacuum pressure is good. what else could cause this problem. car still has plenty of power when driving.
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Old 03-04-2014, 09:49 AM   #2
dawson1112
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You could have a faulty ECT sensor. Responsible for telling the computer what the engine temp is. If it is bad it could be telling the computer that it is warmer than it actually is causing it to have a hard time maintaining idle when cold.
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Old 03-05-2014, 11:08 PM   #3
samltheriault
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im spacing out a little bit but where would i find it. nice car btw
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Old 03-06-2014, 05:39 AM   #4
dawson1112
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Right there on the passenger side of the engine in the coolant tubes front of the engine.

Click the image to open in full size.
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Old 03-06-2014, 09:10 AM   #5
samltheriault
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oh ok thanks ill check that asap. aside from that is there anything else it could be. maybe a bad ECU?
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Old 03-06-2014, 09:32 AM   #6
dawson1112
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Is the car storing any codes? That is the first place Id check .

I highly doubt its the ecu, but it could be you have shorted a wire out in the nip and tuck possibly causing a ground issue or something
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Old 03-06-2014, 10:03 AM   #7
samltheriault
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thats what im hopping its not.... ill scan it and get back to you. later today
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Old 03-06-2014, 10:46 AM   #8
samltheriault
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ok so this is what i got. also keep in mind that my whole EGR system has been deleted for years now and i have driven it many times since then. never through codes till now. so im leaning more towards the first code

KOEO test codes

15 - power interruption to computer memory or EEC. (PCM) keep alive memory (KAM) test failed 2. EEC (PCM) read only memory (ROM) test failed

26 - mass airflow (MAF), Vane airflow (VAF), transmission oil temperature (TOT) sensor out of range. (have a STD transmission)

31 x2 - EVP or PFE circuit below minimum voltage 2. (deleted, confused)

85 - canister purge solenoid failure (deleted)

84 - EGR vacuum regulator circuit failure 2. (deleted)

im assuming its the first two considering my EGR system is deleted completely. not only that but my volts seem to be RPM dependent. I'm running a Powermaster 140 amp single wire alternator. i have the power wire from the alternator running to my battery thats located in the back. should i wire that to my starter relay instead? maybe the system isn't holding enough steady power for the computer to hold memory. if that makes any sense. sorry if i seem to be getting real technical and possibly loosing my mind lol.
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Old 03-06-2014, 12:14 PM   #9
dawson1112
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At this point we only need to look at the code 26 for MAF since we know that you do not have a VAF .

You could try cleaning the MAF sensor with some MAF spray or if you are carefull you can use a little rubbing alcohol and a q-tip you just have to be carful that you don't break one of the elements. I suggest the spray you can get it at any auto parts store. Also check to make sure your air cleaner is not plugged up, and is in good working order.
If you have one of the reusable oil saturated filters like the ones that come with most cai systems, the oil that is used in the filter tends to get pulled up into the MAF and can create issues.
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Old 03-06-2014, 11:12 PM   #10
samltheriault
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alright ill do that then get back to you asap. probably tomorrow night. but thanks. lets prey this will do the trick lol
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Old 03-06-2014, 11:12 PM
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