technical help please 95 5.0 at the end of my rope lol

nubbyless

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Hi i have a 95 mustang vert 5.0 H.O. 5spd idle is erratic sometimes it idles 650 to 700rpm perfectly smooth then randomly starts surging up and down then sometimes it will race up to 2000rpm without touching anything stay there
for 30 seconds or so then fall back down and start surging again then smooths out.

While driving sometimes while driveing at a smooth even speed suddenly it feels like another cylinder or two came on sudden surge of more power then
drops back to normal.

things i have done checked for vacume leaks cant find any unless under the intake havent removed that yet

parts changed all original brand new parts
pcv valve and filter
air temp sensor
coolant temp sensor
iac valve yes mtorcraft
tps
egr and egr sensor
cap rotor plugs wires and coil (tried multiple caps rotor wires)
fuel pressure regulator
fuel filter at tank
driver side 02 sensor

things not changed
fuel pump (pressure seems fine)
ignition module had it tested at pep boys on their computer tested good 12 times in a row
distributor is there any way i can check it
passenger side 02 sensors
maf i did clean it though
is there something else im missing in this list

i did the proper idle setup procedure including letting it idle for 10 to 15 minutes to learn its idle
i hate just throwing parts at it like that but i dont care at this point i just want it to run correctly.

Any ideas
 
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ttocs

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You say the fuel pressure is fine, what is it at? Have you smoke tested it to look for vac leaks?
 

evilcw311

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Yes please explain how you vacuum tested?!? How did you clean the maf?!? Have you checked it for any codes??


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nubbyless

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I have nothing to smoke test just tried spraying carb cleaner and water everywhere waiting for idle change I also changed many of the vacuum lines ones I could get to clean maf with maf spray twice no codes on reader and no engine light
 

ttocs

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smoke test is easy to do there are a bunch of videos on youtube that show how to do it with a cigarette and a bottle. Also how did you check fuel pressure?
 

ttocs

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also curious, were you using the obd2 port on the console to pull codes like everyone tries to the first time?
 

ttocs

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hey I asked cause I did it the first time I tried to check codes. It was 1994 when I did it but I did it and was all confused.
 
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nubbyless

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Tested with odb1 test port on passenger shock tower port works it goes through the tests fine fans kick up etc. For fuel pressure I used a fuel pressure test gauge connected on the Schrader valve if I remember correctly it was 43lbs at idle with vacuum line off. I will look into the smoke test with the bottle and cigarette I live in Florida near Tampa area
 

evilcw311

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Well crap, kinda far to drive and help. Lol

Start with smoke test and let us know how that goes.


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dcm0123

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The sudden increase to 2000 rpm may be caused because the computer sensing something is out of bounds so it increases the speed to compensate for it.
You may want to try turning in the throttle plate screw which sets the minimum opening about 1 turn and see if it helps. Turn it in, turn off the car and restart so everything resets itself.
I had problem with surging idle and it was because the plate was open to far so when the computer tried to increase the idle, it overshot the desired speed, then it would drop back down, then repeat.
 

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