Idle Issue, pulsating idle, lights dimming, etc.

[SMJ325ix]

I start up my '89 325ix in the cold and for a while the idle pulsates, up then down, up then down,...
while it does this and the idle goes way down, the headlights dim, then come back up, dim then come back up.
(does this when its warm as well but its not nearly as bad)

You give it some gas it sounds ok, no pulsating, you let off the gas, and you're back to the pulsating issue again.

I changed out the ICV a while back, earlier this year with an NOS one. Ran fine, but its developing this problem now.

Could it be the ICV went bad?...or more like a bad alternator, voltage regulator, or ECU??

Anyone else ever had this issue?...

Thanks in advance!

[Northern]

I doubt it is the voltage regulator or alternator, unless youre having battery charging/power issues that arent caused by the low idle. Ecus rarely go bad, and since your ivc is new, I doubt it is that either.

I would vote vacuum leak. Check your intake boot for cracks/holes and do a smoke test if the boot is ok.

[dirty30]

Mine had the same issue but the OBC would randomly reset itself and it also had a random slow crank. I found the rear ground for the battery loose on the body so I cleaned the connection, installed a new ground and now everything is fine. The lights still dim slightly at idle but it cleared everything else up. I'd start with new grounds at the engine and the battery. Remember a visual check won't always suffice when it comes to the integrity of these old ground cables. Hope this helps.