I've been having a rough idle issue for a while, but gradually getting worse. Cleaning the TB and MAF doesn't seem to affect it much. I've tightened the intake manifold. It seems to be fairly smooth on a full tank, then degrades after a day. It will be smooth when the engine is cold or cooled off from a short shutdown then soon goes back to rough, so I guess that means it is only in closed loop mode.

My 2010 Base has 76k miles on it, runs top-tier fuel, and I use a mild injection cleaner every couple of months. What else are common causes of rough idle?

I don't know if any of this could be related:
- stumbles/cuts out on light load between 50 - 55 MPH
- think I hear engine knock on light load at moderate speed
- burn .5 qt ~3k miles (seems highway speeds increase consumption)

 

Did you remove the TB when you cleaned it so you can de-crud the back behind the Throttle Plate and the Throttle Plate Evap bypass?

You may need to run it on a scanner from cold to closed loop to see what it is doing, you may have a PCM programming glitch unless an 02 sensor is out of whack.

 

Yes, I removed the TB to clean anything I could see.

At cold, the O2 has a slow but nice oscillation. At hot, it can vary. Sometimes it has a lazy oscillation (stretched out a little longer than when cold), sometimes it will have long peaks with short valleys. I did notice that during the curve peaks the idle sounds louder.

I also noticed the idle hunting a bit. I can't feel it, but can see it on the scanner. It constantly fluctuates within 5 and 10 RPM with that range moving up or down.

 

Well, it just did it again. I was at half a tank and idle was rough. I filled up and cranked up and it was smooth.

 

I just got a letter for my 09 bad throttle pos switch they will fix it free.