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Thread: flat spot problem

  1. #1
    Member extra_anchovy's Avatar
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    Default flat spot problem

    I've had a flat spot for a really long time and taken it to many mechanics who could never fix it.
    Recently I swapped my engine hoping that the problem was confined to the old engine.
    After I put in the new engine in ran great for the first couple days, but then I noticed the flat spot creeping in again.
    It's very occasional and not as bad as before but it seems to be getting more frequent and worse the more I drive it.
    Since I now know it's not the engine, any ideas what else it could be? Or more importantly how to fix it? Would taking it to a place with a dyno be able to pinpoint the problem?

  2. #2
    Veteran slide86's Avatar
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    Default

    The amount of information in this thread is overwhelming.....My brain just cant process it all.

    - What car?
    - What engine?
    - Is it carby or EFI?
    - If its EFI, are you using stock engine management?

    Id replace the fuel filter first.

  3. #3
    Noooob
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    Default

    At what rpm, worse when hot it cold.

    Be nice guys , with your posts and lets get some more info and help him
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    Veteran Skylar's Avatar
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    Default

    It's not like Huw's post was overly offensive and he does post something which will help get to the cause of the problem. The dude is asking for help and should provide as much detail as he can if he wants a decent reply. It's not like you go see a doctor and say "fix me up, doc" cos that's not going to get anywhere, wastes his time and pisses him off. If one were to say "I've suddenly got this pain around where my appendix is and it's also swollen around that area", the doc's gonna know what it is and treat you for it.

    I'd like to help but there's nothing specific I can suggest that's going to help him any great way other than make the guy jump through hoops and replace everything that could cause a flat spot.

    On a humorous note, I'd like to ask, is it a volkswagen or audi that between 3 and 8 years old? That's the first thing that came to my mind after reading the first post.

  5. #5
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    Yeah hues post was fine it was more a warning not to post stupid stuff
    Ae86 Drivingclub - Toyota AE86 Car Club where AE86 | KE70 | Toyota 86 / GT86 | Subaru BRZ | Scion FRS owners

  6. #6
    Member extra_anchovy's Avatar
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    Default

    sorry for not posting all the info, it's just that I made this thread several times before so thought that people are already familiar with it
    it's an Toyota AE86 Trueno GT Apex with a blue top engine from an AE82
    what do you mean stock engine management? as in ECU? if so then I think it's stock
    already tried replacing the fuel filter, tps, spark plug leads, o2 sensor and many other parts including the whole engine
    it probably happens usually around 3000-4000rpm in 2nd or 3rd gear. car runs worse when cold
    not sure if this is related but is it supposed to idle at 800rpm all the time?
    Its usually at 800rpm when I first start but after i drive a bit then stop at the traffic lights or something it usually goes up to 1200rpm
    sometimes up to 1500rpm but after 30 seconds or so it will lower again to around 1000-1200rpm
    also this may or may not be related the water temp sensor is always showing the coldest temperature on a digital guage
    very occasionally it will rise maybe 1 unit above the bottom but quickly go back to the bottom
    also there are hoses blocked off with screws in the throttle body and no cold start injectors
    would taking it to a place with a dyno be able to pinpoint the problem?
    Last edited by extra_anchovy; 21st June 2013 at 11:15 AM.

  7. #7
    Senior Member 4A-GE Power's Avatar
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    Default

    What about dizzy rotor, cap and ignition coil/igniter?? Is the coil getting a solid 12v at all times? Alternator good??

    I'd say its probably got something to do with all those vacuum hoses blocked off you mentioned! Sounds like they've blocked off the cold start/idle up valve.

    Possibly something a miss with TVIS if its still connected????
    Last edited by 4A-GE Power; 21st June 2013 at 02:06 PM.

  8. #8
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    Is a long shot but my old mans ae82 was like that for ages turned out to be a collapsed cat for the hesitation.

    The idle is normal and has to do to with the wax pellet idle control
    Ae86 Drivingclub - Toyota AE86 Car Club where AE86 | KE70 | Toyota 86 / GT86 | Subaru BRZ | Scion FRS owners

  9. #9
    Veteran Skylar's Avatar
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    When Matt says:
    I think he means that that behaviour is normal when you delete the idle up valve under the throttle body assembly.

    When you replaced the engine, did you replace every sensor on the engine? Did you replace the wiring harness also? My feeling is, replace the coolant temp sensor, they very rarely fail but it sounds about the cause of your problem. Does it idle/rev up/cruise fine otherwise?

    This flat spot, is it like a loses power but still gets through it or falls on its face and back on like you took your foot off the gas on a high comp engine then floored it again? Does it misfire or stutter, fast or slow?

    Is it worse when you WOT through it or does it do it when you're trying to cruise at that RPM or lightly accelerate? At what throttle is is it worst/most likely to happen?

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