Thread: Help with troubleshooting high idle/"dieseling"

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  1. #1 Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    Tried all i can think of and can't figure it out. Im running an 02 bottom end with a top swap from a 97.

    Anyways my problem is when i'm driving after i let off the pedal from accelerating the rpms will drop down to about 1600 rpm, and stay there until i brake which then will drop under 1500 and eventually stop at 1100 rpms. I have to push pretty hard as the cars trying to push through the brakes. After i'm stopped for a while it idles down to around 750 rpms. BUT, if i try to take off to fast the car lurches almost dies and the takes off. The car also seems to run rich/er

    Things i've done to try and fix this is obviously
    -check for vac leaks
    -replace MAF
    -change front 02
    -Take out rear 02 so it reads just oxygen
    -Change ICV

    On another note im running SD headers and i also have an exhaust leak. Theres a 2.5in band clamp on the first joint which is slighty too big, and im running just the u bolts on all other connections. Im also getting some KR too where i don't think i should

    When i first had the tune done i don't remember it doing this, and there was definatly 0 knock.

    Any help is greatly appreciated! This car is starting to really piss me off!
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  2. #2 Re: Help with troubleshooting high idle/"dieseling" 
    GrandPrix Junkie machinegunsquid's Avatar
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    Who tuned it? Have them look at the tune again and see if there are any telltales.

    You've changed the IAC Valve? Did you clean out the area the pintle rests against in the TB? My car did the same thing (little higher RPM though) Ended up pulling the IAC valve (new) and cleaning the Throttle body out really well, fixed it.

    "**** bills. You can live in your car but you can't race your house" -dsmuts
    Want her to stop when she's not looking karate chop her in her crotch that should quiet her for a bit or at the very least put a smile on your face -REDCOMPG
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  3. #3 Re: Help with troubleshooting high idle/"dieseling" 
    Moderator dsmuts's Avatar
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    You need a 2.25" band clamp for the exhaust
    98 GTP modded 1.9's, sd headers, 3.4", zzp 1.0 230K miles scrapped.
    04 Comp G zzp stb's, UMI ta's, Speedbuilt sways, bully flo heads, XP, zzp headers, fsic, thrasher shift kit, 60#, 2.6" corsa 2.5", Inferno hood
    01 gt z7 turbo tep trans zzp motor
    08 g8 gt cam exhaust 11.87@118
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  4. #4 Re: Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    I still need to clean my throttle body, but this morning it was -2 and the problem didnt seem to be as noticeable or prevalent. Perhaps temps have an impact on it.
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  5. #5 Re: Help with troubleshooting high idle/"dieseling" 
    Killa Bee Scottydoggs's Avatar
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    sounds like the tb is dirty or the cables are hanging up.

    if you un hook the cables, fire it up, see if it idles right. then slide the throttle cable in and out to feel for it sticking.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  6. #6 Re: Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    Well just got done cleaning the throttle body. The throttle plate was loose so I tightened that up and cleaned the carbon off...didn't seem to make a difference so I might need a new throttle body, or something else is going on.
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  7. #7 Re: Help with troubleshooting high idle/"dieseling" 
    Killa Bee Scottydoggs's Avatar
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    was the plate dragging the TB or showing any wear to the TB or plate? that will cause mare air then it wants to be sucked in at idle.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  8. #8 Re: Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    Yeah, I tightened it up but I'm assuming it just loosened up again.
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  9. #9 Re: Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    I did some more thinking on this. If it was the butterfly being stuck causing more air to come in, then why would it idle down from 1100 to 750?
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  10. #10 Re: Help with troubleshooting high idle/"dieseling" 
    Killa Bee Scottydoggs's Avatar
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    it just takes longer for the flap to close when its sticky. or has carbon build up.

    have ya cleaned it up yet?

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  11. #11 Re: Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    Yeah i cleaned it. Got all the carbon off, especially around the plate. I tightened up the plate too.
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  12. #12 Re: Help with troubleshooting high idle/"dieseling" 
    Killa Bee Scottydoggs's Avatar
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    and its sill acting up like described? no change?

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  13. #13 Re: Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    Correct. I might have noticed a change at the very beginning, but if it did it went back to what it was doing before hand.
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  14. #14 Re: Help with troubleshooting high idle/"dieseling" 
    Killa Bee Scottydoggs's Avatar
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    were the flap screws actually loose? if so re check them. if they are loose again thats probably the issue.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  15. #15 Re: Help with troubleshooting high idle/"dieseling" 
    GT Level Member natethegreat's Avatar
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    ok, Ill check em again and loctite them.
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