XSeries-forum

I have seen this fault code before on a 5 series though (same engine as yours) he was getting poor starting and erratic tick over
The diagnostics pointed to P1632
Defective or weak vehicle battery
Damaged alternator or generator
Loose or corroded battery terminals
Faulty voltage regulator module
Broken cable connections in the charging system
Faulty earth connections
Problems with the battery management system (BMS)

The issue we traced was poor earth connections replacing the engine earth straps and a new battery fixed it

Thanks for your help!
Your on point!
I installed a new battery couple days ago...
Ground straps I added a couple additional several years ago. The ground strap around the motor mount is a negative battery cable for a lawn mower! This has worked in the past!
The latest culprit is the throttle body and the three nipple connection in back of the intake.
I've capped off all three nipple.
I've got an aftermarket tb at the garage we'll see if that erases the surging idle.
Thanks again...

A day later... It doesn't

The uncontrollable rough idel...
Can't drive the car...

I figured it out!

It's the cats!
At 240k the cats are dead...the catalytic converter is clogged.

That's whats causes the surge...hunting surging!

Damn!

OK. So how did you find out it’s the actual issue? Sensor data before/after Cat? Interesting to know how that feeds back into the engine controller, and in my mind, why no warning or message to that effect?

I would have expected a Check Engine Light, and bad emissions but the engine would keep running fine? Not having experienced such, and driving mostly electric (or occasionally diesel) these days.

Intrigued.

When an engine misfires, it dumps raw, unburned gasoline straight down the exhaust pipe. That liquid fuel hits the white-hot honeycomb mesh inside the catalytic converter and literally melts the passages shut.The Misleading Code Trap: This is exactly how codes trick you! When the exhaust is completely choked out, the engine cannot draw in fresh oxygen. The vacuum inside the intake drops to zero. The engine computer (DME) watches the airflow freeze, assumes the electronic throttle body blade is malfunctioning because the air values make no sense, and slams the dash into an EML limp mode surge loop while throwing those misleading 2786 and 2787 throttle codes!

Concerning the video at the start, here's the answer to that "hunting" idle...I make the install tomorrow!