94 SC400 idle problems and accelerating by itself, throttlebody butterfly valve? - ClubLexus - Lexus Forum Discussion


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94 SC400 idle problems and accelerating by itself, throttlebody butterfly valve?

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Old 07-14-12, 10:21 PM   #1
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Default 94 SC400 idle problems and accelerating by itself, throttlebody butterfly valve?

Hey guys, I have a bad idle SOMETIMES. I tried cleaning the iacv but of course the screws are stripped.
I removed the entire intake to clean the intake part of the throttlebody and noticed that the first butterfly valve was fully open and the second one was closed. Is it supposed to be open or is one sticking?
Also when I am driving the car seems to be accelerating by itself. Not much, but enough for it to keep the same speed when I let off the throttle instead of coasting to a stop.
Thanks for any help guys, you dont have to provide a direct.answer for everything,.just let.me know if its supposed to be open and what can be the reason it.is accelerating by itself.sometimes.
My throttle cable does have slack btw.
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Old 07-18-12, 08:36 PM   #2
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The first butterfly is traction control. It is normally open.

I'm still fighting idle issues with my car. It wanted to idle at 3k for a week so I parked the car. Cranked it one day 3 weeks later and it dropped to a solid 700. Dunno how or why. I've cleaned my IAC and even had the ECU rebuilt with not much effect on idle.
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Old 07-18-12, 09:05 PM   #3
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Sounds like idle air control is stuck or throttle butterfly is stuck, try cleaning it
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Old 07-18-12, 10:20 PM   #4
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Thanks for the response guys, I cleaned the iac. And its still happening :l
Could a rough bearing in the iacv cause this? The smaller one was fine, the second bigger one a little rough compared to the smaller one, but not bad in general.
Maybe i reassembled the iacv wrong? When i put it back together I screwed it all the way down.
Will try taking apart the entire throttle body apart and cleaning the other butterfly valve, thanks again guys.
Any more suggestions?
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Old 07-18-12, 10:22 PM   #5
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Also, when I reset the ecu the issue wont happen until the next day. Would it be.bad to reset the ecu everyday just to avoid having this problem? Will my fuel economy get worse if I reset my ecu everyday? My gas mileage is already pretty bad.
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Old 07-20-12, 05:16 PM   #6
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Help? Going to try the fuel ecu.mod
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Old 07-21-12, 04:14 PM   #7
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funny thing is, my 94 sc400 is doing the same thing, and is trying to accelerate by itself when i come to complete stop. Kinda like once i stop and let my foot of the brake at a light, it picks up real fast, which i think it should not. I also tried adjusting tps, and cleaned idle air control valve, and replaces vaccum hoses just for hell of it, and i still get high idle on a second start up. I say second start up because if i let it sit overnight and start it up, it will usually drop alittle but stll lil high, but if i drive it for like 30mins or more and then shut it off and turn it back on, the rpm jump to 2k, and sometimes 3k. This problem been doing this for awhile, and i brought new maf and still no fix. Seems like mystery problem for us.
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Old 07-21-12, 04:18 PM   #8
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I also brought a new ecu for car, and with that, it came with it seems a egr problem or my old ecu wasnt putting out the code bc it was faulty, and with new ecu it prob is showing actual cel now. I may go to pick and pull and hopefully find egr on car their and see if it fix high idle, or do delete method.
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Old 07-21-12, 11:34 PM   #9
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Its so annoying, whats your idle when its acting funny?
Mine is at 2k, and then 1100rpm when in drive.
Have you tried cleaning the throttlebody?
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Old 07-23-12, 05:46 AM   #10
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Yeah i cleaned throttle body with throttle body cleaner a week ago, didnt look nasty in the inside when i took it off, but i cleaned anyway. After little cleaning of throttle body, i went ahead and adjusted my tps sensor alittle, and it brough idle down only for lil bit, but to me it seems like its still not idle right like a good running sc400. Next week i am going seafoam/sparkplugs/oil change/caps/rotors and maybe 2 new ignition coils, and take trip to pick and pull and get a egr valve because my new ecu is throwing that code now for some reason. I may just get old one repaired just to eliminate off the list. I dont know what the hell it could possibly be the high idle, maybe water pump or timing belt? When i drive though, the idle is fine, but if i park it like i said before, it will go from 2k to sometimes 3k.
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Old 07-23-12, 05:49 AM   #11
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Also when i drive the car, their is some whistle like noise coming from in the engine bay area. Sound can be heard from inside the car, mainly through ac vents. I know it sound crazy, but it seems everyhting is connecting to this dam high idle. Wish someone may know the solution.
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Old 07-23-12, 11:11 AM   #12
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Maybe the whistle sound is a vacumm leak? I dont what what it could be either, I mean I havent checked the resistance.on the iacv or the tps, but i doubt this would be the issue.
I have been thinking about seafoam, but i just did my wires and.plugs so i dont wanna go through that again haha.
Try removing the egr completely, then using a resister to prevent it from throwing a code.
I noticed that when my car is accelerating by itself that when i floor it it hiccups a bit and then starts speeding. But this only happens in first gear. But when the car is acting normal i can floor it and no hiccups.
This car is weird.
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Old 07-23-12, 11:12 AM   #13
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Wait is yours high idle the entire time, like even on a fresh morning start or sometimes like mine?
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Old 07-23-12, 07:59 PM   #14
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it Idles high after I take it from a drive, but if I wake up in morning, it will not idle high. Also I got my car at the shop, and told them too see why my car trys to accelerate by itself from a stop, like stopping for a light and high idle thing, and I'll post if they tell me anything. I really don't want to start adding nice stuff to the car until I get it operating right car is good with everything else, but its these dam little problems to stop a whole mess of things I want do with the car.
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Old 07-23-12, 08:01 PM   #15
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same thing also with the hiccup to with mine, if I try floor it, it will do that also. lol we basically have same exact symptoms.
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