5.0L (1979-1995) MustangTechnical 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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car idles rough for a bit then runs fine. need help
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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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.
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)
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.
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.
Alright so i just did a KOER test and these are the codes i got
12 - idle out of range. (high) - im assuming that this is because im not running a stock camshaft and the timing is more advanced then factory
21 - coolant temp sensor out of specified range or ECT out of range
41 - HEGO sensor voltage low/system lean. no HO2S switching detected - i believe that 41 is the right side. correct me if im wrong
30 - DTC not available - looked it up and it said something about cylinder 3 being out of balance?? don't know how its possible to detect that.
now the only thing i don't understand is that the KOEO test code 26 stats that the MAF is or transmission oil temp sensor is out of range. how could that be true if the cars (seems to run/rev fine) after a min or two of feathering the gas??? im thinking that maybe because of KOEO code 15 "power interruption to computer memory or EEC( PCM) keep alive memory (KAM)test failed 2. (EEC) (PCM) Read only memory (ROM) test failed." the computer isn't supporting enough memory to keep the MAF in spec. could this all be causes due to insufficient power circulation. which would go back to the way my single wire alternator wire is hooked up. (to the batt pos terminal in the back instead of the starter relay?) sorry bout the novel and i appreciate you hangin in here with me lol
Did you do the Koer with the engine at full operating temp?
The engine needs to be at operating tempreture to do this test . And the ecm needs to have gone into closed loop.
that coolant temp sensor out of range can mean that it thinks the car is much colder than it is or much hotter than it is . There will be no 02 switching until the car goes into closed loop, because it relies on the ECT to give information on engine temp to adjust the air/fuel mix. The engine must be at least 180 degrees Fahrenheit for the ect to pass the KOER.
ill redo the test again i had it running for a good 10-15 minutes before i did the test and the temp at normal operating temp. but to make sure ill redo it. and ill def try switching over the o2 sensors as well. my ECT sensor was moved due to my HVAC delete. its in one of the coolant passages in the back of the lower intake manifold. i had to since the heater core lines were deleted as well but its still generally in the same spot just out in back of the engine. ill post a pic in a bit
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