Car has rough random idles suddently ... OBD

[Voltmaster]

My car ( 06 corolla CE ) has rough idle at start up and very very little randomly starting today.

AC system also throttle downs while my engine shakes like crazy for first 5-10 min of driving. Works perfectly fine during driving.

NO CHECK ENGINE LIGHT. I was wondering what should I look for in OBD data in order to try and narrow it down? I have USB one i can connect to my labtop and read data of ECU.

I dont believe the car will give any misfire data... So not sure where to look for.

Cant find any leaks in any fluids or any other abnormalities.

Thank you very much!

 

[RoGuE]

I used to have a rough idle in my Taurus. I put a can of Seafoam through the vacuum line and it helped some. I guess it had some carbon buildup.

 

[eljefino]

What happens if you give it a slight amount of gas? Is the idle rough because it's really low? What if you shut it off and restart it again?

If I had to venture a guess, your TPS is going out of calibration *WHILE DRIVING* and a restart would "fix" this. Without the TPS saying "idle", it chooses to pursue a low and shaky idle speed. You may see this on your scanner but you may not.

 

[Pete]

You might try cleaning your idle air control (IAC) valve. Your symptoms sound similar to a common problem in Gen-1 Siennas. I'd recommend Seafoam Deep Creep as a cleaner

 

[HerrStig]

Originally Posted By: Pete
You might try cleaning your idle air control (IAC) valve. Your symptoms sound similar to a common problem in Gen-1 Siennas. I'd recommend Seafoam Deep Creep as a cleaner
The pesky IAC doesn't (as they say) "throw" a code every time. Sounds like it is not providing extra air when the compressor is engaged. It's at the worst at idle.

 

[01rangerxl]

Originally Posted By: HerrStig
Originally Posted By: Pete
You might try cleaning your idle air control (IAC) valve. Your symptoms sound similar to a common problem in Gen-1 Siennas. I'd recommend Seafoam Deep Creep as a cleaner
The pesky IAC doesn't (as they say) "throw" a code every time. Sounds like it is not providing extra air when the compressor is engaged. It's at the worst at idle.


X2!

Totally different vehicle, but when my truck's IAC got funky, it would idle around 500 RPM which is about 250 RPM too low. It never set a code.

 

[PandaBear]

Might want to post this in the Mechanical / Maintenance forum instead so more people can help.

 

[Bill in Utah]

Originally Posted By: PandaBear
Might want to post this in the Mechanical / Maintenance forum instead so more people can help.

And moved...

 

[yonyon]

I agree with Pete as far as the IAC being a good suspect, but prefer a different remedy.

-Get some [whatever's cheapest] brand throttle body cleaner in a spray can with a straw. Loosen up a clamp or whatever so that you can use the straw to "Tssst Tssst Tssst Tssst" inject a little cleaner into the fresh air hose in super short bursts until the can is empty. This will clean out the throttle body and the IAC. You might need someone to operate the throttle pedal to prevent stalling. Do not be surprised if this turns on the check engine light, just turn it off and don't worry about it.

-If that doesn't help the IAC might be just plain old dead.


Originally Posted By: Voltmaster

NO CHECK ENGINE LIGHT. I was wondering what should I look for in OBD data in order to try and narrow it down? I have USB one i can connect to my labtop and read data of ECU.


Coolant temperature is always worth looking at in the case of low idle.