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03 mach 1 chasing idle surge gremlins...

Discussion in 'Mach 1' started by texas_snake, May 22, 2018.

  1. texas_snake

    texas_snake Member Established Member

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    I am trying to tack down idle surge issues. The idle has randomly been staying up or jumping up (one time at almost 3k). I know these cars have an IAC issue and there are restrictor plates out. I have one and it didn't really change this issue. I also feel hesitation when driving. I pulled the IAC and it drove much better (but needed to be careful not to stall it, it idles at about 650 with it unplugged and can dip when slowing down).

    I have done quite a bit already on this:

    * New MAF (one of the screws was stripped out, only leaving one screw).
    * New air filter
    * cleaned throttle body (these throttle bodies look pretty bad after 75k I would say). Or at least mine does
    * Checked tps (showing .96 dc volts and goes past 4.5 at WOT)
    * I disconnect the battery to reset idle controls and let it run for a while (everything off), then for a while with everything on.
    * The IAC looks fairly new (I am the 3rd owner). But cleaned anyway.
    * But... when I pull the IAC when acting up, it goes to 650 and behaves. So I believe the IAC is at least the symptom, but I don't know if it is the cause (but looking likely).

    I am trying not to just guess with new parts. Any way to actually test the IAC? Otherwise I am thinking new IAC, and if not that, throttle body. But starts to add up if I am wrong.

    Thanks.
     
  2. my04mach

    my04mach Member Established Member

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    I’m interested to see what you find. I had some issues with a slow or struggling ignition that happened 75% of the time (no rapid VROOM with ignition). Also, I had occasional idle issues similar to what you experienced. I went through and checked and replaced my spark plugs. My COP’s seemed fine. No misses or shark bite type issues, so continued with my usual routine (dab of dielectric grease in COP boot). I’ve read before where they say you can’t clean the IAC, but o did anyway. I ended up buy a new Motorcraft IAC from RockAuto. The symptoms didn’t get better and in fact seemed worse. I believe it was a bad IAC.

    Anyway, I swapped the original back in. I took off my JLT cold air kit and put the stock one back on and all my symptoms cleared up. Maybe my JLT kit was a bit leaky. I had checked for leaks while troubleshooting after swapping in new plugs, but it seemed fine. It was really surprising that the Motorcraft IAC was bad, so watch out if you need to buy one.


    IG: @ab_mach1
     
  3. 98 svt

    98 svt Premium Member Premium Member Established Member

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    Who makes the IAC? The aftermarket IACs have always been hit or miss.
    My vote goes for swapping in an oem IAC
     
  4. texas_snake

    texas_snake Member Established Member

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    The IAC is OEM Ford. But I agree. Got to go with the obvious at the moment and that is the IAC (since the issue goes away or stops surging when I unplug it while running). Will update when I have it installed. Fingers crossed at this point.
    Thanks.
     
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  5. texas_snake

    texas_snake Member Established Member

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    OK. Got the part, did not change things. It is the Ford part, put it on, pulled the negative terminal to reset the computer. It idle fantastic for a bout 15 min (turned on A/C and headlights half way on the time), but then the idle started going up, first to 1200 rpm, then if I rev'd it, stayed at almost 2k. Pulled the tps and things went down.

    So I know if I pull either the tps or the iac, it will go away. Also if I restart the car, goes away for a bit. So this makes me think it is not a vacuum leak.
     
  6. 98 svt

    98 svt Premium Member Premium Member Established Member

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    Have you checked the voltage at the TPS with a multimeter? They are adjustable
     
  7. texas_snake

    texas_snake Member Established Member

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    Yup. Sitting at .97 volts and 4.65 at WOT. This is with engine off, key on.

    Can you measure the volts with the engine running or does that ground out the green wire for the computer in some way. I have only seen info on testing while key on/engine off
     
    Last edited: May 26, 2018
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  8. 98 svt

    98 svt Premium Member Premium Member Established Member

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    Yeah, that's all I've ever done too.
     
  9. jmontes04

    jmontes04 Member Established Member

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    Mine is doing the exact same thing, except mine will go up to 3k rpms, i was told to check the crank sensor, itll drive fine, and as soon as i push down the clutch to coast, the idle goes way up and stays there


    Sent from my iPhone using the svtperformance.com mobile app
     
  10. texas_snake

    texas_snake Member Established Member

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    So mine is bouncing around a bit. Some times it will stay at 1200, then 2k if I rev it up (comes down and stays higher). To me, I think something is telling the IAC to do this.

    * If I pull the IAC, it goes away for a bit
    * If I pull the tps, it goes away for a bit
    * If I restart the car, goes away for a bit

    Does not feel like a vacuum leak. But not ruled out.

    Wondering if it is something with the A/C, speed control. Not sure on crank sensor.
     
  11. texas_snake

    texas_snake Member Established Member

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    OK, one thing I noticed when cleaning the Throttle body is that it seemed to be open a bit. I could see some light through it on top and bottom when in the dark with a flashlight and I expected it to be more closed. So I had this on my list to check.

    I saw this video which is very helpful -->

    I checked the screw on the TB and it has been moved about 1/4". I clearly see the blue loctite. Also my base idle with IAC unplugged is 700 which is too high per that video. This would cause the IAC to be closed most likely, but it should idle with partial open allowing the IAC more control.

    So I will look to adjust that, reset the computer by pulling the negative for 30 min and then stepping on brake for 30 seconds. Will see what that reset does.
     
  12. Mike's03Mach

    Mike's03Mach Active Member Established Member

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    I had a 2000 GT a few years ago that had an idle issue. After a few weeks of messing around with things and cleaning the IAC, I just bought a new one and that fixed my problem.
     
  13. texas_snake

    texas_snake Member Established Member

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    It had a new IAC and I tried a new IAC (from Ford) and did not fix things so far. We will see where adjusting the idle per the video guidance gets me. It was clearly messed with by the previous owner.
     
  14. Mike's03Mach

    Mike's03Mach Active Member Established Member

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    If you said that in this post, I missed it. Hope you figure out what the problem is.
     
  15. texas_snake

    texas_snake Member Established Member

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    Reset the throttle body screw and reset the KAM memory to test from scratch. Still get the idle sticking from 1000 to 2500 rpm when it hit open loop. With blue driver I could see the long fuel trim on the bank 1 way out of range (between 15 to 20) which I believe is compensation for a big lean condition. The driver side was also around 8 to 15 which is high when the idle went up. During warmup it was acting perfect. Trying to get more data, but seems I likely need to track down a vacuum leak.
     
  16. SVTdreamin04

    SVTdreamin04 What's a "Termi"??? Premium Member Established Member

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    Yep, sounds a lot like unmetered air getting into the engine. Prior to my rebuild, I had these issues as well and it was due to bad 02 sensors


    Sent from my iPhone using Tapatalk
     
  17. texas_snake

    texas_snake Member Established Member

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    Found the issue!!!

    May not be the last one, but at 75k miles, this factory throttle body is shot. When I cleaned it I could see pitting and the surface could just not fully clean. And I had noticed the plates seemed more open than normal. Remember I just bought this 1 month ago and I knew it had a high idle issue. Recently I found the throttle plate screw had been advanced quite a bit. I set it back and was having a worse issue with high idle (really became undrive-able for safety). It was also running lean at idle with long trim stats. Today started it and had the issue right off the bat (normally seemed more when warm).

    So I decided to get out and press on the throttle in the direction of closed. idle came right down. Rev hard, no issue, rev light, high idle. Sooo........... the issue is a sticking throttle plate (100% certain). When gentle throttle, it does not return to the setting most of the time and can be as high as 3k. When hard throttle it mostly returns/snaps back. This also explains why the genius before me turned up the screw. They tried to avoid the sticking at the last part of throttle travel. But in doing that, they threw off the IAC and computer control and it drove with hesitation and stick would stick sometimes. A/C on only slight improved the idle coming down.

    So I am ordering a new throttle body. Sadly 2 weeks back I suspected the throttle body, but only from inspecting it. Did not think it was sticking, but now proved it. I even tested it with the gas pedal and cruise disconnected since it has the zip tie mod on the gas pedal. But still sticks. So this is my issue. Hoping this is the last problem for the throttle response. So far new mass air (1 of the 2 screws was broken off) and now new throttle body.

    Fingers crossed I am done...
     
  18. SVTdreamin04

    SVTdreamin04 What's a "Termi"??? Premium Member Established Member

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    Awesome! Glad you found it.


    Sent from my iPhone using Tapatalk
     
  19. texas_snake

    texas_snake Member Established Member

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    Since the factory throttle bodies are out of production (likely would be pricey anyway), I just ordered a accufab 60mm setup. Will see how things work out.
     

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