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Sc300 Backfiring On Idle Rough Idle NO CEL!

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Old 04-04-13, 07:38 PM
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mikevandam
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any updates?
Old 04-04-13, 07:40 PM
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SC400slide
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Did you ever try replacing the o2 sensors, or do you not have any of those either? lol
Old 04-04-13, 08:25 PM
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ScWift92
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Originally Posted by SC400slide
Did you ever try replacing the o2 sensors, or do you not have any of those either? lol
no check engine light so doubt it idk what it could be might be the pump its self also i wonder if the 12v mod is doing it???
Old 04-04-13, 08:52 PM
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SC400slide
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You might of done the 12v incorrectly, could be fuel pump, could be IACV, could be ECU...has your CEL ever gone on? Mine actually went out so IDK if there is a CEL on.
Old 04-04-13, 09:25 PM
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ScWift92
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Originally Posted by SC400slide
You might of done the 12v incorrectly, could be fuel pump, could be IACV, could be ECU...has your CEL ever gone on? Mine actually went out so IDK if there is a CEL on.
idk it was on due to grounds but now cleared also could it be rotor from the distributor or my fuel pump i need solid answers remember it only back fires on idle which means no load
Old 04-05-13, 07:21 AM
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Originally Posted by ScWift92
idk it was on due to grounds but now cleared also could it be rotor from the distributor or my fuel pump i need solid answers remember it only back fires on idle which means no load
If it only backfires on idle, I'd probably elluminate the choices of the ECU, fuel pump, parts that matter when the engine is throttled. Sounds like something small now...more like a broken main vacuum hose, or maybe even the TPS or IACV. Seems as if it could be the distributor as well...read this.

https://www.clublexus.com/forums/per...le-timing.html

GL
Old 04-05-13, 08:42 AM
  #22  
Ali SC3
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revving it up can hide alot of symptoms, but that doesn't mean you don't have the same problem when the motor is loaded. the motor is just a lot more sensitive when its idling to fluctuations. I wouldn't even rev it hard until you fix the issue unless you want to risk breaking something.

its not hard to check the cap and rotor, take it off the cap and inspect it or just replace it if its old and you are unsure. If the edge of the rotor looks very rounded off, or the cap has gouge marks on the 6 pins, where some have alot less material than others, you are probably in need of a new cap and rotor.
When one of them is done, you loose spark on 1-6 cylinders pretty randomly. also when the rotor and cap goes its just a matter of time before all those sparks jumping around the inside of the distributor kill the cam and crank sensors in the base.

From that video there is no way the car can rev properly like that, it sounds like more of a bad knock than a backfire. From the video it sounds like you are not getting spark on all 6, possibly some cylinders are washing down with fuel which slows the motor down and then you get that sound in the video. It could also be an injector or something. you will have to try and pin point it a little more or give us some more info, keep us updated it doesn't sound like a leak to me anymore, cause right after start it idles down just fine, it just can't keep the rythym its either fuel or spark on this one.

*edit* just read you said you changed the cap. if you didn't change the rotor you should, you always replace those 2 together.
also the 12v fuel mod won't affect your idle, the fuel pressure regulator returns the excess fuel back to the tank. It may be noisier than stock but shouldn't change the way the motor runs under normal conditions.

Last edited by Ali SC3; 04-05-13 at 08:50 AM.
Old 04-06-13, 07:29 AM
  #23  
ScWift92
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Originally Posted by Ali SC3
revving it up can hide alot of symptoms, but that doesn't mean you don't have the same problem when the motor is loaded. the motor is just a lot more sensitive when its idling to fluctuations. I wouldn't even rev it hard until you fix the issue unless you want to risk breaking something.

its not hard to check the cap and rotor, take it off the cap and inspect it or just replace it if its old and you are unsure. If the edge of the rotor looks very rounded off, or the cap has gouge marks on the 6 pins, where some have alot less material than others, you are probably in need of a new cap and rotor.
When one of them is done, you loose spark on 1-6 cylinders pretty randomly. also when the rotor and cap goes its just a matter of time before all those sparks jumping around the inside of the distributor kill the cam and crank sensors in the base.

From that video there is no way the car can rev properly like that, it sounds like more of a bad knock than a backfire. From the video it sounds like you are not getting spark on all 6, possibly some cylinders are washing down with fuel which slows the motor down and then you get that sound in the video. It could also be an injector or something. you will have to try and pin point it a little more or give us some more info, keep us updated it doesn't sound like a leak to me anymore, cause right after start it idles down just fine, it just can't keep the rythym its either fuel or spark on this one.

*edit* just read you said you changed the cap. if you didn't change the rotor you should, you always replace those 2 together.
also the 12v fuel mod won't affect your idle, the fuel pressure regulator returns the excess fuel back to the tank. It may be noisier than stock but shouldn't change the way the motor runs under normal conditions.
im gonna order the rotor and i had just got a fuel pump so im gonna replace that aswell
Old 04-08-13, 08:17 PM
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ScWift92
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ok the car backfires once in a blue now that nyc is warmer but on idle the car revs between 600-1000 RPM Im Thinking it could be VSV is plugged up wrong.
Old 04-09-13, 10:29 AM
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Could be the VSV as well I guess, did you ever rule out the TPS?
Old 04-09-13, 09:49 PM
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ScWift92
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Originally Posted by SC400slide
Could be the VSV as well I guess, did you ever rule out the TPS?
idk its most likely an ignition problem it really doesn't do it when warm only when cold.
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