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Discussion Starter · #1 · (Edited)
Hi Guys

I've been searching for a cure for my rough idle for some time now. I've noticed it's quite common on the Pre Lps. Theres quite a few questions regarding this problem but never a happy ending.
Was thinking we could put all our experiences and suggestions on here to finally help put this to bed

I've done the obvious over the past few yrs

Removed throttle boddies and cleaned

New fuel filters

New Spark plugs

New air filters

Repaced Coil packs

Smoke test no leaks



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Discussion Starter · #3 ·
Thanks Mark
When we completed the smoke test we actually took the hoses off from the air box to the throttle bodys and watched the Flaps. No movement from the Flaps and of course the hunting stopped. Had thought about taking the K&N Filters out and putting standard ones in

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Hi Guys

I've been searching for a cure for my rough idle for some time now. I've noticed it's quite common on the Pre Lps. Theres quite a few questions regarding this problem but never a happy ending.
Was thinking we could put all our experiences and suggestions on here to finally help put this to bed

I've done the obvious over the past few yrs

Removed throttle boddies and cleaned

New Spark plugs

New air filters

Repaced Coil packs

Smoke test no leaks



Sent from my SM-G930F using Tapatalk
Pretty common and 90%+ are a result of the throttle bodies being dirty, you do not have to remove them to clean them pull off the air intake wipe down with a white rag an alcohol first, make sure to clean the butterfly using a stiff toothbrush with the alcohol-do not use WD40, brake cleaner works well also. When i did this to mine they looked clean until i wiped them down really took the time with toothbrush, qtips you name it including all the edges. I was replacing the hoses at the time anyway and the filters. problem was 100% solved. A friend of mine had a similar issue everyone told him to buy rebuilt throttle bodies at $3,500 each. I did the same to his and showed him how to it, his was running far rougher than mine and really dirty took a few hours-problem solved ran like new. If after this you still have problem it is possible its an internal issue wit the throttle dirty inside and/or the butterfly blade edge is damage even the smallest imperfection will cause air to pass by. Closely inspect the edge of the blade with a magnifying glass if needed. Unlikely its a sensor or run rough at any rpm
 

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Discussion Starter · #5 · (Edited)
Pretty common and 90%+ are a result of the throttle bodies being dirty, you do not have to remove them to clean them pull off the air intake wipe down with a white rag an alcohol first, make sure to clean the butterfly using a stiff toothbrush with the alcohol-do not use WD40, brake cleaner works well also. When i did this to mine they looked clean until i wiped them down really took the time with toothbrush, qtips you name it including all the edges. I was replacing the hoses at the time anyway and the filters. problem was 100% solved. A friend of mine had a similar issue everyone told him to buy rebuilt throttle bodies at $3,500 each. I did the same to his and showed him how to it, his was running far rougher than mine and really dirty took a few hours-problem solved ran like new. If after this you still have problem it is possible its an internal issue wit the throttle dirty inside and/or the butterfly blade edge is damage even the smallest imperfection will cause air to pass by. Closely inspect the edge of the blade with a magnifying glass if needed. Unlikely its a sensor or run rough at any rpm
Great to know that!

When I said I'd cleaned them I didn't go in with a tooth brush. Just used brake or carb cleaner and a cloth 3rd time lucky?

I took mine out. Sorry cant rem will the butterfly swing both ways (Pardon the pun) to enable cleaning all the way round?

Just thinking if and when next rough idle. Before cleaning. What if I removed the pipe at the tb covered it with high dense foam (which I have) to make an air tight seal. This might give me a idea while the car is running

Btw that's some saving per TB







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So I’ve had the same problem and replaced everything you have plus more.
Plugs
Coils
Fuel filters
Cleaned throttle bodies
Front diff fluid
Tranny fluid
Cabin air filter. What a PIA
What I’ve figured out from putting in seat time is 2 things
It’s all of a sudden seeming to get better. Almost to the point of seeming normal

1. I always would have the heat on since it’s cold and would turn the economy button on since I didn’t want compressor spinning.
I turn economy off and it seems to not surge as bad. Almost like the computer things economy is still on even when it’s off and surges the motor

2. I disconnected batter again thinking maybe this time it will work. I disconnected for about 20-30 min and like I said it seems to be running better???

Also I’m through my 2nd full tank of gas and I’ve been treating with sea foam. Maybe it’s cleaning something???

Who knows
But I will advise as I drive more what I figure out.
 

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So I’ve had the same problem and replaced everything you have plus more.
Plugs
Coils
Fuel filters
Cleaned throttle bodies
Front diff fluid
Tranny fluid
Cabin air filter. What a PIA
What I’ve figured out from putting in seat time is 2 things
It’s all of a sudden seeming to get better. Almost to the point of seeming normal

1. I always would have the heat on since it’s cold and would turn the economy button on since I didn’t want compressor spinning.
I turn economy off and it seems to not surge as bad. Almost like the computer things economy is still on even when it’s off and surges the motor

2. I disconnected batter again thinking maybe this time it will work. I disconnected for about 20-30 min and like I said it seems to be running better???

Also I’m through my 2nd full tank of gas and I’ve been treating with sea foam. Maybe it’s cleaning something???

Who knows
But I will advise as I drive more what I figure out.
Your last clue was the one I thought about today. The G does all sorts of weird things because of the battery connection-i learned that one too. How old is the battery? Would highly changing the ground cable and also cleaning the frame where the ground cable attaches, and bolt if rusty- simple to get the battery out not so simple to get the ground cable out and clean the frame without lifting the car, i did mine in the garage a bit of houdini act but got it done without lifting. I was getting electrical errors replaced the battery and most of them went away then over time they came back. I read on here about it pulled it all apart new cable, bolt, cleaned the frame (that was a mess at the connection) never had the problem again. The battery and rough idle episode took place all the first year i had it and no issues with either in 4 years since. I think it had the OEM cable
 

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Discussion Starter · #8 ·
Excellent tips Guys

I noticed that my idle is better with the heater/AC off! Never tried Econ mode before.

Might pull the battery which I replaced 18 months ago and see if that works.

Actually I'm gonna check the ground connections and maybe replace the ground cable too. Does the under tray need to be removed to get at the ground cable?

Dagofast did you use an OEM cable or generic?

Ive heard great reports about sea spray think def run a can or 2 through the car and see what happens.

Cheers

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Excellent tips Guys

I noticed that my idle is better with the heater/AC off! Never tried Econ mode before.

Might pull the battery which I replaced 18 months ago and see if that works.

Actually I'm gonna check the ground connections and maybe replace the ground cable too. Does the under tray need to be removed to get at the ground cable?

Dagofast did you use an OEM cable or generic?

Ive heard great reports about sea spray think def run a can or 2 through the car and see what happens.

Cheers

Sent from my SM-G930F using Tapatalk
I used a generic cable that was the same length from Autozone-no issues. No reason to remove the undertray unless the car is on a lift, I went through the top/trunk not so easy but doable
 

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Discussion Starter · #10 ·
I used a generic cable that was the same length from Autozone-no issues. No reason to remove the undertray unless the car is on a lift, I went through the top/trunk not so easy but doable
Yea thought so. I rem seeing alot of screws holding the under tray on previously. Think ill swap the ground cable over and buy sea Foam this wkend.



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