Bad Idle Surge on '88 Fox w/Mods

Discussion in 'Fox 5.0 Mustang Tech' started by dangrego, Sep 12, 2009.

  1. hey, this is Dan with a modified '88 fox...tried to do the set-idle checklist, but having chance of sustaining idle with IAC unplugged without lots of throttle...background: Edelbrock RPM perfomer II upper and lower intake, MAF conversion, 24 lb injectors set at 45 psi, 24 lb cal computer and 75 mm MAF meter, 70 mm throttle body, Ford Racing B303 cam, heads were ported and polished w/oversized valves. Vacuum system seems intact. Timing set at 14 degrees. Runs rich as hell at idle (no matter how low I set the fuel PSI) and drives poorly, but has good power at hight RPM, dies real easy taking off from a stop and has a bad idle surge. New non-OEM TPS set at 0.971.
  2. Any Codes present?

    Surging idle can be caused by many things, and even the Surging Idle procedure wont help. I suggest you make sure everything ECM sensor related is fine first. Also put the Fuel Pressure back to 39-40psi with vac off. The fact that you have to lower the fuel pressure and its still rich, indicates a problem elsewhere
  3. replace your engine coolant temp sensor. ive personally seen 3-4 foxes have the same problems and that $3 part fixed it.
  4. going to pull the codes and see, also, i did put in a new coolant temp sensor....i have a jimmy-rigged heating system and so the coolant temp sensor is rigged up and suspended in-line two heater/coolant hoses (does it need to make metal ground-contact with the car maybe?)
  5. Damn, where are you buying your ECT's???

    I gotta get in on that action!

    Ever replace the ECT and find out it wasn't the problem? Basically you just wasted the time/$ of replacing it?

    When did the problems start? Had you just made some changes?
  6. advanced auto :shrug:
  7. man if you figure it out let me know cause i have the exact same problem with my car. i wouldn't say mine has a BAD surge, but it definitely has a surge at idle and runs RICH as hell. i've had it dynoed twice and both times it had a 10.x:1 a/f. every sensor on my car is new too. no vac leaks (i've checked dozens of times), fp is at 40psi, timing at 14. it's strange cause it'll drive HARD on occasion, but i'd say about 80-90% of the time, it drives poorly, just like what yours sounds like, spits and sputters, low power, etc. mine will do this thing after it's warm, if i'm just sitting there idling like at a stop light or something, it'll idle at around 800 with a small 100 rpm surge, but if i sit there longer than a few minutes, the idle will try to drop to like 500 or 550 and gets really quiet. i have to blip the gas to keep it from dying. anyone have any ideas?
  8. No it doesnt use any metal contact for a ground, the ECT needs to be in circulating coolant. Sensor gets its ground from the SIGRTN to operate.
  9. New thread maybe? :nice:

    It will get kinda confusing otherwise, but if its been tuned on the dyno, Id say your startup fuel tables arent set right. Im no tuner, just what I have seen first hand
  10. hah yeah i was actually about to make it into it's own thread. thanks for the info!
  11. I see one for 16.99 and one for 57.19....
    Advance Auto Parts
    (hope the link works)

    $3 would be cool.
  12. $57 thats crazy.
  13. vri-1


    i fail :(
  14. K, well, the ECT isn't the problem then, cause it is in coolant are the codes i pulled with key on, engine off:

    67 O: Manual Lever Position sensor out of range or A/C input high

    95 O: Fuel pump secondary circuit failure

    29 C: Insufficient input from Vehicle Speed Sensor

    66 C: VAF/MAF sensor fault, below minimum voltage OR TOT sensor signal input below self-test minimum, or vane air flow circuit below minimum (E4OD)

    I'm still lost though? And also, my TPS voltage is always jumping around, every time I run the car and shut it off to recheck it, it is always a different reading and by a lot....amperage gauge in the car is showing a draw too, even at high RPM.....any ideas? Not sure how to go about fixing those codes either.
  15. Were these code run with the car in gear?

    Auto or Stick tranny?
  16. manual....and it was in neutral
  17. Ok, you need the Engine Running Codes(aka KOER codes) But Code 67 wont let the KOER test start.

    Two things you can try here to get the codes. One, you can try and hold the Clutch down, and hold it down, then have your scanner hooked up, then crank the car and see if it will start the KOER test.

    If that dont work, then you can try and unplug the white connector on the Clutch Pedal switch, and install a jumper connecting the 2 terminals on the white connector, then crank the car and se if the KOER test will start. KOER test may take a few minutes before it starts to actually flash codes
  18. yah, i tried the KOER 6 months ago and it wouln't do squat....will give this a try...also, maybe i should have mentioned, i gutted out all the A/C 'cause it didn't work, and i like having sweaty balls while i drive :). maybe something needs to be done with a loose end there somewhere/how too? well, back to the car. oh, also, i did install a new higher pressure fuel pump since i changed from 19 lb injectors to 24 lb about 8 months ago too, maybe i messed something up with that?
  19. Try and see if you can get the codes. Thats the number one priority right now.