Rough starting, tach bouncing with car off
 

Very recently starting having an issue with my car where the tach needle jumps up and down from 0-250 whenever the key is in the "on" position. Seems to work fine while the car is running.

Checked the RPMs on the PFC and that also says that my rpms are bouncing even though the car isn't started.

Checked the Diagnostic box under the hood (IG- to ground) and found that I was getting 0-0.5V, again with the car off and the key in the "on" position.

I can hear my ISC buzzing, probably trying to keep the car idling, not realizing that the engine isn't moving.

I suspect that fuel is also being injected under these conditions, as it's half-flooding itself and tough to start

Very low mileage original engine (under 24k kilometers) and no recent modifications done. For 3 months I've had an intake/PFC/SMIC. Problem started 2 weeks or so ago

Something wrong with my CAS? Despite the car working/boosting fine while running? Anything in particular I should be looking for? A specific ground, or...?
Thanks

I wish you would have received an answer

There's still hope :nod:

Any pros willing to donate some Canada day guidance?

maybe you have gone deaf?

Lol Possible, but the car isn't even started. Tach flutters anyway

Anyone? Speedo doesn't move, just the tach

Solved... kind of?
The tach doesn't flutter when power to my wideband O2 sensor is unplugged
It's plugged in here: https://www.rx7club.com/attachment.p...2&d=1156038841

Anyone have an idea why it might be causing such an issue? Not sure if I should be tapping power from elsewhere or digging deeper to see what's up

Got the problem solved
Turned out that my LC-1 wideband was causing feedback due to a common ground with the ECU. My Datalogit is mounted to the back of the PFC, so I guess when I was installing the LC-1 I saw where the ECU was grounded and thought "That must be a good ground or they wouldn't have used it"
Anywho, I moved "chassis ground #2" to a separate bolt and now everything runs great. No more tach bouncing and no more hard starting.

Discrete grounds FTW!