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Discussion Starter · #1 ·
I have a strange problem where if I'm lightly cruising with the rpms at around 1500, and i let go of the throttle, i.e. to coast to a stop the rpms will suddenly drop to under 500 rpms and then bounce back up to about 600 rpms.

sometimes when i'm going a little faster and i let off the throttle, it'll bounce up and down at around 1,200 rpms a few times and then settle down.


This started after I installed the doug thorley long tubes, y pipe and 02 simulator. I had bungled up an air fuel ratio sensor and i replaced that. Btw i'm running the stock exhaust.

I can't imagine any of the exhaust stuff to effect the weird rpm behavior, but hoping someone with more wisdom can offer some insight. Maybe the free flow of the headers and y pipe running into the restriction of the stock exhaust has something to do with it?:simmadown:

thanks
-Kevin
 

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Are the forward o2 sensors close to the same location as they were with stock manifolds? If they are moved farther down stream with the long tubes it could cause a delay in feed back to the ECM causing a rolling idle like you are describing. This is a problem I have seen when modding Mustangs. In the pony car world access to tuning software is easy, the FJ is my first stab at a foreign car. I have not seen any options for user end tuning.
 

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Discussion Starter · #3 ·
hmm i'm not sure about the distance, but the air fuel sensor port is on one of the pipes coming off the cylinder towards the rear, detecting only that one cylinder while the stock sensor would seem like it would detect all of the cylinders. But what you said makes sense, and hopefully it's normal.

thanks:bigthumb:
 

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I wonder if DominicG's obd codes are similar to what you're experiencing. He got the codes after installing the DTs.
 

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Discussion Starter · #5 ·
Mine threw a P0031,same as Toytaco I hope his is different cuz those sensors are $$$$:flame:
 

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hmm i'm not sure about the distance, but the air fuel sensor port is on one of the pipes coming off the cylinder towards the rear, detecting only that one cylinder while the stock sensor would seem like it would detect all of the cylinders. But what you said makes sense, and hopefully it's normal.

thanks:bigthumb:
What you said about the o2 sensor only reading 1 cylinder on the LT's is why most header companies move the sensor bung further down stream, to get a reading across the entire bank that is being metered. The ECM knows what the location of the o2 sensor in the stock configuration and reacts to changes in A/F on a table based on that distance. If you change that distance you need to update the mapping for the time delay.

I wish I could help you in offering tuning product info. I just checked the "SniperTuning" site and they have a Japanese section with no products shown. It may be coming in the future.
 

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Discussion Starter · #7 ·
What you said about the o2 sensor only reading 1 cylinder on the LT's is why most header companies move the sensor bung further down stream, to get a reading across the entire bank that is being metered. The ECM knows what the location of the o2 sensor in the stock configuration and reacts to changes in A/F on a table based on that distance. If you change that distance you need to update the mapping for the time delay.

I wish I could help you in offering tuning product info. I just checked the "SniperTuning" site and they have a Japanese section with no products shown. It may be coming in the future.

Theres the URD MAF calibrator and the Unichip that u can use to tune the Fj.
 

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Theres the URD MAF calibrator and the Unichip that u can use to tune the Fj.
The MAF calibrator wont be any help on the o2 table. That would be helpful if you are FI of have a large CAI. I don't think the Unichip is end user adjustable. I think it is a straight plug and play with a basic fuel/timing mapping upgrade.
 

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Discussion Starter · #10 ·
Nope, Mine still does it even tho I'm back to stock drivetrain wise..
 
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