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  1. #1
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    Ames, IA
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    Default stumbles at cruising throttle.

    Seems like no matter what RPM it's at, the car will stumble/slightly jerk while at cruising throttle, which is basically enough to maintain speed, or lightly accelerate. If I give it some gas or let off the gas the stumble goes away. I only have 1 code and it's for the rear o2 sensor, which does not affect the engine's performance at all. I just seafoamed the engine through a vacuum hose. I'll run another can through the gas tank today. I havent checked the plugs yet, but Id think that would be more of an issue under load, which this is not.
    -Thomas
    2003 SVT Focus Black/Blue - stock except for K&N Panel Filter, SCT X3, and some header wrap.
    1988 Mustang LX Notch - Roadrace chassis waiting for a heart transplant. Working up a 408W w/ direct port nitrous... someday.

  2. #2
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    Default Re: stumbles at cruising throttle.

    Okay, to all intersted *crickets* I replaced the plugs (was going to anyway) and it didn't help. I unplugged the MAF sensor and started the car up. Problem goes away.

    When the MAF is unplugged the computer automatically reverts to open loop, which runs the engine off of preset maps. The MAF and o2 do not send feedback to the computer in open loop.

    So either my MAF is bad, or my o2 is bad. I guess I'll replace the o2 first since it will need done before 90k anyway (at 76k right now) and if that doesn't fix it I'll replace the MAF.

    -Thomas
    2003 SVT Focus Black/Blue - stock except for K&N Panel Filter, SCT X3, and some header wrap.
    1988 Mustang LX Notch - Roadrace chassis waiting for a heart transplant. Working up a 408W w/ direct port nitrous... someday.

  3. #3
    Senior TEAM Member 1svt4u2c's Avatar
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    Jun 2004
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    York, PA
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    Default Re: stumbles at cruising throttle.

    Did you try cleaning the MAF? If you clean it, you might be able to save yourself a few more $$ But if that doesn't work, then at least you tried, right?
    Back in the saddle again.

  4. #4
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    Pocatello,ID
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    Default Re: stumbles at cruising throttle.

    I have this exact same problem with my 02 SVT.
    I also have an intermittent CEL that comes on for the #1 O2 sensor - slow to read code. I clear it as soon as it comes on but the stumble is there whether the CEL is on or off.
    I wonder if it is the O2 sensor since we are having the same problem?
    I will try to clean my MAF as well next week. I also think I have a vac. leak because the idiot before me eliminated the PCV and now only has a hose from the valve cover to the intake pipe and its too big with no clamps.

  5. #5
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    Default Re: stumbles at cruising throttle.

    I replaced my front o2 and cleaned my maf. I even put in a brand new maf and it didn't fix it. For the heck of it I put the stock tune back on the computer and the problem went away. The problem is in my tune. So I'll be contacting my tuner.
    -Thomas
    2003 SVT Focus Black/Blue - stock except for K&N Panel Filter, SCT X3, and some header wrap.
    1988 Mustang LX Notch - Roadrace chassis waiting for a heart transplant. Working up a 408W w/ direct port nitrous... someday.

  6. #6
    Rookie
    Join Date
    Apr 2007
    Location
    Northern IL
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    8

    Default Re: stumbles at cruising throttle.

    How about trying the after market tune one more time?
    How long did you have the other tune on your car before this happened or did the problem occur as soon as you flashed it?

    I am having a similar problem, car stumbles under load, no power, rough idle sounds like an old vw bug. Had a smell of rotten eggs, so I trashed the converter, and installed an ORP. Car still idles rough an sounds bad when hitting the throttle, have not pulled it off of the jack stands yet, so I don't know how it will respond under load. Sounds like it won't.

    Going to try unplugging the MAF like you suggested, to see what happens.
    Plugs are OK all cylinders firing, compression is at 110lbs per cyl.
    Going to try to disable rear O2 sensor(got a preditor w/ Toms tune no problems for two years now).

    Good luck, hope you post your results.

  7. #7
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    Default Re: stumbles at cruising throttle.

    Well when I loaded the 91 performance tune it was there but hardly noticeable. When I loaded the 93 performance tune it was much worse. I didn't associate it with the tune at first because the tuner is very reputable. I'm waiting to hear back from him on his thoughts. I loaded the 89 gas mileage tune today because I was in BF iowa where they only had 89 available. It stumbles just as bad as the 93 performance tune does.
    -Thomas
    2003 SVT Focus Black/Blue - stock except for K&N Panel Filter, SCT X3, and some header wrap.
    1988 Mustang LX Notch - Roadrace chassis waiting for a heart transplant. Working up a 408W w/ direct port nitrous... someday.

  8. #8
    Rookie
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    Apr 2007
    Location
    Northern IL
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    Default Re: stumbles at cruising throttle.

    Well i tried to reflash back to the stock tune and killed the car, when I turn the key every thing lights up but won't crank. Preditor says the program did not transfer, do you want to return original file. tried it five times no success. Time to find the manual.

  9. #9
    TEAM Member
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    Jun 2009
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    Pocatello,ID
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    Default Re: stumbles at cruising throttle.

    Is there a way to tell if your ECU is reflashed?
    I think the previous owner did a flash but I have no idea what it is or who did it. Is there an easy way to reset it back to stock?

  10. #10
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    Apr 2007
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    Northern IL
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    Default Re: stumbles at cruising throttle.

    Got mine flashed back to stock( had to remove two fuses), think the problem with my car is the coil pack. When wire for cylinder number four is removed it has no effect on the motor.

    As for confirming a stock tune, you could always have the stealer do it for you, I'm sure that would be expensive.

    Off to the parts store again.

  11. #11
    TEAM Member
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    Jun 2009
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    Pocatello,ID
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    Default Re: stumbles at cruising throttle.

    as far as I know my 02 has a Hypnotic SCT tune
    how can I get rid of it?
    I think it is causing some of my issues

  12. #12
    TEAM Member IowaSVT's Avatar
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    Jul 2009
    Location
    Eldridge IA
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    239

    Default Re: stumbles at cruising throttle.

    hey bfg before you get a new coil, change the plug. Could just be a fouled plug

  13. #13
    TEAM Member
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    May 2007
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    Tampa(TnC)
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    Default Re: stumbles at cruising throttle.

    Make sure you have fuses 46 and 61 pulled before you try to reflash or it will fail.
    2002 SVT Focus Totalled 1/4/10 R.I.P.

  14. #14
    TEAM Member
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    Pocatello,ID
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    Default Re: stumbles at cruising throttle.

    the problem is I don't have the SCT
    it didn't come with the car
    so can the dealership just reflash it back to stock?

  15. #15
    Senior TEAM Member 1svt4u2c's Avatar
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    Jun 2004
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    York, PA
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    Default Re: stumbles at cruising throttle.

    Bump.

    Hey ThomasA, how are ya making out with this?
    Back in the saddle again.


 
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