Rough idle after warming up

BRANDONMJESSIE01

MEMBER
2006 CHRYSLER 300
3.5L
V6
2WD
AUTOMATIC
151,000 MILES

When I have let my car get warmed up and it has been driven, it seems to hesitate while idling at stop lights. It idles around 650 RPM but it will intermittently drop to roughly 500 RPM and the entire car shudders then it immediately recovers. I recently changed the plugs and air filter in the car. I also cleaned the throttle body, MAP sensor, and the air temperature sensor. The spark plugs were torqued to spec with a torque wrench and the same for the intake manifold. I have checked the EGR valve for leaks and I cannot find any. Same with the vacuum lines. I sprayed starting fluid around and was not able to find any places where the starting fluid was able to enter the engine to change the idle. I have a scanner and I do not see any codes, I have no check engine light. I am at a loss for trying to figure this one out.

Thank you in advance.

1 Reply

CARADIODOC

MECHANIC
33,870 POSTS

Since you have a scanner, look at the live data for the "Idle steps", or "AIS steps" Normal is somewhere around step 32. The first thing to do is observe what that changes to when the low idle speed occurs. If it goes up when idle speed goes down, the Engine Computer is trying to raise idle speed, but without success. If the number goes up when idle speed goes up, the computer is reacting to other sensor data. We'll need to look at those and see what doesn't look right.

If you find the step number to be "0", the computer lost its memory at some point when the battery was disconnected or run dead. Operating characteristics and fuel trim numbers will be relearned as you drive, except for "minimum throttle" That requires a specific set of conditions for the relearn to take place. Until that is done, the engine may not start unless you hold the accelerator pedal down 1/4", you won't get the nice idle flare-up to 1500 rpm at start-up, and it will tend to stall at stop signs.

To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.