Funky Idle

[Porquer]

My 2.5 seems to have trouble idling. It will idle at what seems like a normal RPM (no tach) for a while, then the RPMs drop and it sounds like it’s struggling to run. Then, after a little bit, the RPMs rise back to normal. Also smells like it’s running rich. I can see the idle stop moving as the RPMs cycle from high to low. I let it run for a bit with the TPS unplugged, and it behaved exactly the same. I tightened all of the manifold fasteners and there was also no change. The rhythm from high to low RPM seems fairly consistent. What are some things I can check to troubleshoot?

 

I have a video, but it’s too large. What’s the easiest way to share it?

[eaglescout526]

How are your grounds?  Start with the basics. 

[Porquer]

13 minutes ago, eaglescout526 said:

How are your grounds?  Start with the basics. 

Where are the sensor grounds on the 2.5? I know about the ground strap from the engine to the fire wall, but isn’t there single place on the block where all of the sensor grounds attach?

[eaglescout526]

The ground for the sensors and ECU ground out at the dipstick mount stud or bolt. 
 

Hopefully we can eliminate electrical being an issue before we look to mechanical. Part of me thinks headgasket is failing as I had similar symptoms but let’s check the free and less labor intensive stuff first.