kleecker

I have had my '08 for 2 years now, done the basic maintenance (OEM plugs, filters, fluids).

Starting quite a while ago, every rare occasion, the idle would dip down from it's normal of 600 rpm to about 450 rpm. It's easy to tell, as you feel the chassis vibrate.
The issue didn't usually last that long (well under a day). Yesterday it came back and lasted all day, and into this morning. So this morning, the problem is still there, I decide to look under the hood (everything is up to temp), dunno what else to do (NO codes being thrown). I can hear the thermostat go on and off in unison with the fans, but that is about it.
I drop the hood, get back in the car, and the idle is back to normal. wtf? Gimme a code to work with, but no.

on, had to replace #1 coil about a year ago.

Any ideas?

18TTony

The reason why ther Check Engine light is not coming on is because the problem is "fixing" itself...............Hook up a code reader to the DLC and see what codes are "PENDING"

OBD codes that have NOT MATURED are stored in the "Pending Codes" location on an OBD scanner when this happens, the Check Engine light will NOT come on.

OBD codes that have MATURED are stored in the "Permenant Codes" location on an OBD .....when this happens, the Check Engine light WILL come on.

Note: I would suspect EGR Valve related problem........but without a code, that is pure speculation.

kleecker

great. The only times I have looked at pending is immediately after I have (hopefully) taken care of a code which set the CEL light, and have cleared all codes.


I guess there is no set answer for how long a pending code stays there? That it depends on the code itself?
Now days after the problem has "disappeared", I'm wondering if I should expect to see a pending code related to this, or if I have to wait again until the problem comes around again, and connect soon after problem starts.


Thanks.

18TTony

Hmm.....if no pending codes.........you could look in the HISTORY location on your scanner if possibile............most inexpensive scanners don't have this capability though. Of the four scanners that I own, only one is capable of displaying Code History.

Something you could try when the idle is low is:

Hook up a scanner and look at the LIVE DATA......specifically, the TPS Monitor info. At idle, the TPS voltage reading should display 1 volt or slightly under. If voltage is 0.75 or less, chances are you have a defective TPS sensor. At idle TPS Percentage should display 11.4%

TPS is just a potentiometer........with a bunch of tiny electrical blades inside it. Various underhood temperatures can have an effect on thier operation when TPS start going bad.

Also, look at the ECT (engine coolant temperature) infomation with the scanner while the idle is low......a bad temp sensor could also have a bad effect on engine idle.