Help me create the "Surging Idle Checklist"

Discussion in 'Fox 5.0 Mustang Tech' started by jrichker, Apr 10, 2005.

  1. Why isn't this thread a sticky anymore?
  2. It is.

    See Daggar's sticky of all sticky's " Useful Technical Thead Index" at the top of the 5.0 Tech form. Inside are all sorts of great tech notes and upgrade information. I think this method of collecting all the good tech notes in one place s a great idea.
  3. I'm gonna go out on a limb here, and sound stupid for a minute. is the IAC and IAB the exact same part? All through these posts I've heard people referring to cleaning the IAC in one post and cleaning the IAB in another post, one person saying the IAC is the thing on the front of throttle body with wires, and the picture labeling that same part as IAB. So, yeah I'm a little confused.

  4. The IAB and IAC are the exact same part.

    Ford changed what they called it sometime in the early 90's. It did not change the part or its function, just the name to conform to the emerging SAE standard for all motor vehicles.

  5. Be sure you read the very first two posts in this tech note. That's where all the tests and fixes are posted.
  6. From my original post at:

    After being directed here by jrichker, I went through about 7 of the steps, at which point i got bored and went to something else... my hideous cooling fan wiring harness. This consisted of a generic fan wiring harness from advance auto, and an additional 5 prong relay. Being as I have a 2 speed fan from the late model 4.6L, it was running low speed based on the thermometer lodged in the radiator fins, and flipping on high speed with the A/C. Wires were all over the place, and ugly colors too, so I did some cleanup work and also wanted my low speed to run constantly when engine is on. I ripped out the harness and wired my own setup with two 5 prong relays. I was able to unscrew the ground screw for my high speed relay by hand with a socket. After the rewire, my car has not stalled once while running with or without the A/C on. Apparently the sloppy ground for my A/C relay was the cause.

    I still have a problem I've had pretty much since I bought the car. Very frequently after the car warms up, I can turn it off, and when I crank it back up it has idle problems and will stall. After I re-crank, and give it gas for a bit(10-15 seconds) the idle will smooth out and run on it's own. Any ideas? I've already cleaned my TB, IAC, MAF, Air Filter, replaced fuel filter, and I'm about to go pick up a brand new IAC from the dealership.


  7. Mine surges bad too, Mine is a S/C car. Since I installed the S/C it doesnt want to idle It will idle like at 500 RPMS till either I rev it up and it will hang up there for a few seconds and then fall and die OR it will idle at 500 then die either way DIES any suggestions, I read the list and the only thing I havent tried is the elbow that goes to the S/C but I have a power pipe that replaces that elbow
  8. Try clocking the MAF (rotating the MAF housing). Sometimes that helps place the MAF sensor inlet in smoother flowing air so that it gets better airflow and makes more accurate readings.
  9. ok I will try that...also the car just started poping at idle every few seconds , sounds like in the exhaust, could this be the culprit of the idle or is it running lean at idle
  10. What did you get when you dumped the codes?
  11. I have a surging idle for the first two minutes when the engine is cold. (No surge in temps above 80) Had that since buying the car.
    From your list, the only steps that list cold idle problems are the IAC and base timing. Are there any other things I am missing in regards to a cold idle only? I have an F cam and I'm starting to think it may be a rich/lean condition that may need a tune for open loop.
    (BTW new IAC, air/water temp sensors, and 12* timing, some backfiring into the intake under load only if engine very cold)
  12. Thanks for this thread Jrichker

    If your having crazy issues with your throttle sticking or idle staying higher than what it's set at, try loosening the 2 TPS screws a little.
    EDIT: maybe that wasn't my entire fix! also check your throttle plate screws to make sure they haven't loosened and when you tighten them MAKE SURE your throttle blade is not binding with the throttle bore!

    History: I have been hunting down my intermitent sticky throttle/high idle problem for about a month now, since I bought the car. The car seemed alright but ran very rich. Thanks to this forum I figured out how to dump the codes and found out that I needed a to adjust the TPS because it was out of range. It first measured .002. I did some adjustments but could only get it to .68 even after widening the holes with the dremel. That's when it started: intermitent sticky throttle/high idle (what I mean by this is RPM's would stay at the RPM it was when I pushed in the clutch or drop very slowly, put it in gear and the car would increase speed with out me touching the gas, idle wouldn't return to to base while stopped at a light - sometimes 1200/ most of the time 1800, seemed like the idle was possesed and did what ever it wanted to). I would try different things: clean TB, IAC, MAF, Filter, new TPS and kept checking range after I did different things, base idle adjustments, even found 2 vacuum leaks - one on a broken vacuum cap and another on the bypass tube for the supercharger (boost is great now!) All these things seemed to help a little but the problem would keep coming back, sometimes better sometimes worse. Codes were always: 15 - SCT chip causes this, 85 - CANP not connected/ smog removed, 95 = Fuel pump briefly lost power or something like that.

    I was reseting the base idle at 900 and after I did I readjusted the TPS, disconnected the battery and reconnected the IAC. When I started the car back up I let it idle for about 2 minutes to start relearning and the idle wouldn't drop below 1200. Maybe it just needed more time to learn -so I went out for a little ride. It was a little better but still wasn't right. When I got home I grabbed the throttle linkage with my hand and could slightly move it back - idle would drop right back to 900. Flipped the throttle and again it stuck around 1200 and would not drop on its own. Something had to be sticking! WTF!! I've already rerouted the throttle cable, checked the throttle plate when I was cleaning it, everything! I loosened the 2 TPS screws a quarter turn thinking maybe they are binding the throttle plate and the idle went right back to base idle. Flicked the throttle and right back to base idle. Took it out for a ride - perfect! Maybe the aftermarket TPS's are a little bigger than factory?
  13. My dad picked up a well used '91 GT a year or so ago. The car had 169K miles on it and had idle issues. Mainly high idle, we did a 10 minute tune up and set the timing. This fixed a few issues but not the high idle so I turned my attention to the IAC. It had a ton of carbon and gunk in it so we tried to clean it with the normal spray methods to no avail. The valve just would not seal due to all the buildup.

    I said what the hell let's take it apart and clean the plunger and seat. We found out that the metal end cap does nothing but keep you from taking it apart. We cut 2 small slits in the cap 180* apart to allow it to easily be removed like a bottle cap. Underneath metal cap it a plastic cap that screws in, unscrew it with a pair of needle nose pliers. You can then remove the plunger and cleanup everything good as new. If you don't mess up the metal cap too bad you can put it back on so it looks like its never be messed with.
  14. I have something to add to #16 but I have to give a brief background of my surging. My car is a 1994 5.0 GT with simple bolt ons and a full MAC 2 1/2" exhaust with shorty headers. I had a bad surging idle problem until I replaced my IAC (or IAB) sensor. After the IAC replacement I had an intermittent surge that I could correct simply by revving it once (tap the gas and it would calm right down). Then while fixing something else I realized timing was at 8*... I bumped it up to 12*(running 89 octane) and I have not had any sort of surging since.

    I think 8* isn't enough and 10* should be the minimum. My car ran much better and sounded smoother after only changing the timing from 8* to 12*. I'm sure 10* would have done almost the same thing because that's what they were set with from the factory, but I went straight to 12*.
  15. just gettin in on the great info.
  16. Not Sure What To Do?

    This is a great thread! My only problem is that it has grown so big that I am getting mixed up on what to try next. Can somebody please direct me in the correct direction on what to try? I have a 94 GT with a 306ci, AFR 185's and a stage 3 cam (kinda big). When the car is idling correctly it is at 900 RPM. Lately on cold starts it surges between 900 and 1100 RPM for about 15 seconds and then idles correctly. I give the car about 1 minute to warm up and then take off. When I put the car into gear and take off it wants to stall by idling low. By the time I get down the block it is fine. The car will idle fine for 5 minutes of stop and go and then start to act up when it is warm. Then the idle will surge at 900 then 1100 then 700 and lower and lower until it stalls on me (It never surges over 1100 RPM). I did recently replace the IAC. Was I supposed to reset anything when doing that? Any suggestions? :stupid:
  17. The first two posts contain all the fixes, so you don't need to read the whole thing to fix your problem fix.

    A word about the checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work your way down. Jumping around will possibly cause you to miss just what you need to see to find and fix the problem. Don’t skip any steps because the next step depends on the last step working correctly. [/b]
  18. printer not working so subn