Voltage Drop and Lights Dim when Coming to a Stop

[CHI2000GTP]

Looking for some tips into what could be causing this ongoing issue that I'm experiencing in my 2000 Turbo Prix. I have a previous post on here form a few days ago where I'm experiencing ignition issues. That issue is now fixed and the car is driving but maybe the two issues are related?


Whenever I'm coming to a stop, whether pressing on the brake pedal or just coasting to a stop, my voltage drops like a rock. At idle is stays constant at 14.3 or higher. When driving it's around 14.2v or higher. When coming to a stop however, the voltage drops to as low as 9.8v. I have a quick, 20 second video of it happening below. Watch the Aeroforce in the top right corner. Numbers jump from 14.2 > 10.8 > 13.5 > 14.1 > 11.1 > 13.7 > 11.2 > 14.1 ...etc


Things I've done already:
Scrubbed, sanded, scrapped all grounds. EXCEPT for the under carpet grounds in the cabin.
Replaced IAC sensor with brand new AcDelco sensor
Cleaned MAF sensor


VIDEO:

Voltage Drop. - YouTube

 

[FordMan77]

Have you had the alt checked? Wonder if the voltage reg. is on its way out.

 

[bandook]

I would stop in AutoZone or your preferred shop and have your battery and alternator tested.

 

[ItHurtz]

Alt is 5 years old. Have you tried taking the zzp booster off?

 

[CHI2000GTP]

Yesterday I put in the spare new battery I have, made sure it was 100% charged. Also put in a nice new stud for the positive terminal.

No Change.

Booster is next.

 

[CHI2000GTP]

Removed ZZP Voltage Booster - No Change


Next up is an alternator swap, and going to go ahead and replace ignition switch/harness.

Also, I've done some reading and it appears that a bad brake booster could be causing this. Doesn't look like a fun job.