IS350 rough idle issue
12-02-20, 12:47 AM
#1
Pit Crew
Thread Starter
IS350 rough idle issue
Hi members
I recently noticed my IS350 engine idle rougher at around 600 RPM and with slight vibration in drive mode with AC off. The engine would idle smoothly again as soon as I turn my AC on and the RPM by raise at around 700 RPM. It's the same in eco, normal, sport and sport+ mode in both M and D. I have recently cleaned my engine using CRC intake valve cleaner and Royal purple fuel injector cleaner with oil and filter change. I have also reset my ECU by disconnection the battery about 2 weeks ago - now driven about 700+km. the only thing I done differently this time is I over filled my engine oil by about 200ml and it's wasn't looking too overfill from the dip stick. I have scanned my car and came back with no code. Does anyone know what might be the cause of rough idle with AC off?
See video link https://youtu.be/Q8mBl-bfiMw
I have following powertrain modes: RR Racing ECU tune, F-sport full airintake system with custom hole cut at lower intake airbox, Full CAT back invidia Q300 exhaust system.
I recently noticed my IS350 engine idle rougher at around 600 RPM and with slight vibration in drive mode with AC off. The engine would idle smoothly again as soon as I turn my AC on and the RPM by raise at around 700 RPM. It's the same in eco, normal, sport and sport+ mode in both M and D. I have recently cleaned my engine using CRC intake valve cleaner and Royal purple fuel injector cleaner with oil and filter change. I have also reset my ECU by disconnection the battery about 2 weeks ago - now driven about 700+km. the only thing I done differently this time is I over filled my engine oil by about 200ml and it's wasn't looking too overfill from the dip stick. I have scanned my car and came back with no code. Does anyone know what might be the cause of rough idle with AC off?
See video link https://youtu.be/Q8mBl-bfiMw
I have following powertrain modes: RR Racing ECU tune, F-sport full airintake system with custom hole cut at lower intake airbox, Full CAT back invidia Q300 exhaust system.
Last edited by gamma113; 12-02-20 at 11:09 AM.
12-02-20, 07:22 AM
#2
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Unfortunately there seems to be an issue with the video link...I notice the url says "studio.youtube.com"...which I've never seen before.
What's the year and mileage on the IS?
As part of the intake cleaning was the throttle body cleaned?
When you switch the A/C on it's common for the idle to drop slightly as it's putting load on the engine...however 600RPM is on the low side.
With the RRRacing Tune I believe they do not recommend using an aftermarket intake...of course other than their carbon fiber intake tube.
One test could be to remove the tune and put back the stock program and see what happens. If the issue resolves itself, then it's just the tune.
What's the year and mileage on the IS?
As part of the intake cleaning was the throttle body cleaned?
When you switch the A/C on it's common for the idle to drop slightly as it's putting load on the engine...however 600RPM is on the low side.
With the RRRacing Tune I believe they do not recommend using an aftermarket intake...of course other than their carbon fiber intake tube.
One test could be to remove the tune and put back the stock program and see what happens. If the issue resolves itself, then it's just the tune.
12-02-20, 11:13 AM
#3
Pit Crew
Thread Starter
Unfortunately there seems to be an issue with the video link...I notice the url says "studio.youtube.com"...which I've never seen before.
What's the year and mileage on the IS?
As part of the intake cleaning was the throttle body cleaned?
When you switch the A/C on it's common for the idle to drop slightly as it's putting load on the engine...however 600RPM is on the low side.
With the RRRacing Tune I believe they do not recommend using an aftermarket intake...of course other than their carbon fiber intake tube.
One test could be to remove the tune and put back the stock program and see what happens. If the issue resolves itself, then it's just the tune.
What's the year and mileage on the IS?
As part of the intake cleaning was the throttle body cleaned?
When you switch the A/C on it's common for the idle to drop slightly as it's putting load on the engine...however 600RPM is on the low side.
With the RRRacing Tune I believe they do not recommend using an aftermarket intake...of course other than their carbon fiber intake tube.
One test could be to remove the tune and put back the stock program and see what happens. If the issue resolves itself, then it's just the tune.
I sprayed into the throttle body when doing the intake valve Cleaning. I could check if it clean. Will it be worthwhile to clean both throttle body and MAF sensor?
RPM is lower at around 600 with AC off and higher 700+ with AC on. See link https://youtu.be/Q8mBl-bfiMw
i didn't have this issue until after recent CRC intake valve Cleaning with resetting ecu.
12-02-20, 12:55 PM
#5
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12-02-20, 01:00 PM
#6
But I would then follow Sasnuke suggestion on the tune (or anything else for that matter) after that.
12-02-20, 01:33 PM
#7
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I sprayed into the throttle body when doing the intake valve Cleaning. I could check if it clean. Will it be worthwhile to clean both throttle body and MAF sensor?
RPM is lower at around 600 with AC off and higher 700+ with AC on. See link https://youtu.be/Q8mBl-bfiMw
i didn't have this issue until after recent CRC intake valve Cleaning with resetting ecu.
RPM is lower at around 600 with AC off and higher 700+ with AC on. See link https://youtu.be/Q8mBl-bfiMw
i didn't have this issue until after recent CRC intake valve Cleaning with resetting ecu.
If you look closely at the numbers it's about 660RPM with the AC off, and about 750RPM with the AC on.
The ECU will naturally idle up the engine when you turn the AC on, which it is doing, so everything is working like it should.
With the throttle body cleaning, I open the flap by hand (with the vehicle off of course) and spray the back of the flap as well as the front.
Then I get a rag out and draping it over two fingers on one hand (usually index and middle), and while holding the flap open with the other hand, I clean the back of the flap and most importantly, around the edge of the flap. The front is easy enough to see and clean.
At that point i turn the rag to a clean spot, with the flap open still, and clean the aluminum bore above and below the flap.
If done correctly there should be some very obvious black stains on your rag which is the carbon that has built up.
You can then hold the flap open and spray a little more to get any final carbon off.
On the next startup it will likely stall and/or run rough, and likely smoke a little...which is all normal.
You could disconnect the ECU again before starting to clear any learned values.
Take it for a drive after to blow any last bits of the chemical out and see how it idles now. I can almost guarantee that it's going to be better.
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waleedj3is (12-16-20)
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12-02-20, 01:57 PM
#8
drives cars
Yeah the idle RPM looks similar to how mine was. A/C on, RPM goes up to just over 700. Just under 700 with it off. Slight difference, but enough to cause a difference in the amount of vibration. I'm with Sasnuke on giving it a little Italian tune-up. 
12-04-20, 03:18 AM
#9
Pit Crew
Thread Starter
I was able to copy/paste the link to get the video going.
If you look closely at the numbers it's about 660RPM with the AC off, and about 750RPM with the AC on.
The ECU will naturally idle up the engine when you turn the AC on, which it is doing, so everything is working like it should.
With the throttle body cleaning, I open the flap by hand (with the vehicle off of course) and spray the back of the flap as well as the front.
Then I get a rag out and draping it over two fingers on one hand (usually index and middle), and while holding the flap open with the other hand, I clean the back of the flap and most importantly, around the edge of the flap. The front is easy enough to see and clean.
At that point i turn the rag to a clean spot, with the flap open still, and clean the aluminum bore above and below the flap.
If done correctly there should be some very obvious black stains on your rag which is the carbon that has built up.
You can then hold the flap open and spray a little more to get any final carbon off.
On the next startup it will likely stall and/or run rough, and likely smoke a little...which is all normal.
You could disconnect the ECU again before starting to clear any learned values.
Take it for a drive after to blow any last bits of the chemical out and see how it idles now. I can almost guarantee that it's going to be better.
If you look closely at the numbers it's about 660RPM with the AC off, and about 750RPM with the AC on.
The ECU will naturally idle up the engine when you turn the AC on, which it is doing, so everything is working like it should.
With the throttle body cleaning, I open the flap by hand (with the vehicle off of course) and spray the back of the flap as well as the front.
Then I get a rag out and draping it over two fingers on one hand (usually index and middle), and while holding the flap open with the other hand, I clean the back of the flap and most importantly, around the edge of the flap. The front is easy enough to see and clean.
At that point i turn the rag to a clean spot, with the flap open still, and clean the aluminum bore above and below the flap.
If done correctly there should be some very obvious black stains on your rag which is the carbon that has built up.
You can then hold the flap open and spray a little more to get any final carbon off.
On the next startup it will likely stall and/or run rough, and likely smoke a little...which is all normal.
You could disconnect the ECU again before starting to clear any learned values.
Take it for a drive after to blow any last bits of the chemical out and see how it idles now. I can almost guarantee that it's going to be better.
Thanks for your help. I managed to fixed the problem by cleaning my throttle body and disconnecting the battery. I use ODB2 reader to read my RPM. prior to cleaning my idle RPM without AC was 560 and with AC on was 700. After the cleaning and a short driving my engine is now idling smoothly at 650 RPM without AC on. I was amazed by amount of dirty and black carbon found inside my throttle body. Although my IS350 has only done 68,000 km. The culprit to rough idling was certainly the carbon and dirt deposit inside the throttle body. See photos below:
As you can see the inside plate of the throttle body is black full of carbon deposit
The edge of the throttle body plate is full of carbon deposit after cleaning the front and back facing plate.
Amount of dirt and carbon come out onto the towels
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Sasnuke (12-04-20)
12-04-20, 03:20 AM
#10
So the car should be idling at 600 rpm? Mine idles at like 1200-1400 lol
12-04-20, 03:30 AM
#11
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Thread Starter
I am not sure, I am sure someone else can chip in. My is350's idle feels buttery smooth now and it feels like what a lexus IS should be. Before my rough idle and vibration feels like a old Honda civic
12-04-20, 05:33 AM
#12
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With AC on and the rad fans going, you will be closer to 1000RPM, but it should never be any higher.
12-04-20, 05:43 AM
#13
When I am in drive it drops below 1000 rpm, when I am in park it's 1200-1400 rpm. Should I take it to the dealer? I still have my powertrain warranty I think
12-04-20, 06:04 AM
#14
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If you don't have a check engine light on, it may be a little tougher to figure out the issue.
Also, when you shift to Park, I would suggest giving the throttle a blip first to give it a chance to settle and see if it's still idling over 1000RPM.
In some cases there could be carbon buildup around the flap preventing it from closing properly, which could cause the idle to be higher.
12-04-20, 08:58 AM
#15
Instructor
Mine was idling a bit high and rough and doing that fixed it.