1st time I4 owner, does yours idle smooth?

[HotRod53]

I have a bit of a rough idle, and it may be normal, maybe I'm not used to an I4. It's smooth a silk above the 750 RPM idle, but not as smooth as I think it should be at idle while in gear. In Neutral, it's fine.

I have already cleaned the throttle body, I did gain 3 MPG, I'm just not sure that it is as smooth as it should be.

My definition of smooth is like a V6, can't even tell it's running.

[doingwork]

I think I4 motors are naturally a bit rougher. I think I remember reading somewhere that V6s are by naturally the smoothest motors. When I'm at a stoplight the motor might feel a but rough, but when I'm outside the car there aren't any funny noises so I don't worry.

2011 LE 6AT


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[speedkar9]

From an engineering standpoint, V8's and V6's are naturally smoother because their cylinder configuration allows the cancellation of opposing vibration forces; whereas when the cylinder's are inline (such as I4), the forces don't quite cancel but add up, making it seem rougher and noisier.

My 03 I4 is a bit "rough" at idle (i.e. you can tell that the car is running at a stop light), whereas in the V6 Sienna, you can't hear or feel anything, its so smooth!

[HotRod53]

I completely agree with your Engineering description, and once I hit anything over idle, it's smooth as silk. Sounds like it's just a matter of not knowing what to expect from an I4.

It runs like a top, I'm working on getting my mileage up, I've already cleaned the throttle body, I guess it is what it is. You're right, no weird noises, just a little vibey at a light. When I read that there was a TSB for balancer pulley issues, I thought that may be it, I since read that it is a V6 issue only.

[Glenn8963]

as near perfect smooth as possible.

[leakyseals]

Been a slow process with my I4 but getting better. Now it only shakes/idles rough occasionally when ac/fans are on, etc. Unlike before its able to correct itself idling up "most" of the time. It seems to be a "skip" more than a rough idle. Put your hand over the exhaust when its doing it you will see what I mean. There is a gap in exhaust air. Weird. I did all the basics, tuneup, etc. I even rotated a new coil through, no change. Getting rid of sludge and running a thinner synthetic really helped. Getting new coolant in there really helped too.

There are 3 things I suspect could be the cause, going to address each at a time so I know what resolved it.

1) The throttle body cleaning worked some, but I have searched over the past year and quite a few people have replaced the throttle body and the idle issue was resolved. Because they are electronic not mechanical, they can just fail. I plan to take it completely apart in the spring to check for motor wear. There is an issue where the motor can get stripped, so the TB plates don't close tight. Also a dealer tech told me shooting TB cleaner into the IAC hole wont work, there is natural obstruction that requires manual cleaning. Won't know till I open it up.
2) Oxygen sensors. That skipping feeling at the exhaust can be a rich/lean mixture issue. May as well replace them when I manually clean the cat in spring.
3) ECU programming. On many TSB for cat replacement, sulfer smell, etc. there is modification to the ECU programming. Just like our computers they find things, and with a DBW throttle body I can imagine scenarios where all this ties into the idle.

Maybe this will be helpful, let me know what you've tried. Its a head scratcher. But its unacceptable. Probably will sell it and get a v6 if I can't resolve it. I have an old corolla in the family that has its own set of issues, but idles great so its something about this engines setup, not toyota I4's in general.

[HotRod53]

I've done the TB cleaning by removing the snorkle and cleaning with a rag, toothbrush, and spray. I've run Techton thru it and I'll probably put new Iridiums in it very soon, I'm at 93K. Dealer wanted $10.50 each! Rock Auto here I come.

It's not unbearable, heck I don't idle much anyway....LOL. Knowing what I know now and given the choice, I would have held out for a V6.