Electrical problem
1994 BMW 325 6 cyl Two Wheel Drive Manual 116000 miles
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I noticed a couple of weeks ago that when the car is idling and i role down all four windows at the same time the tachometer dropped. Also while driving when i turn the fog lights or brights on the needle also drops and jumps. What could be the problem? Bad battery or alternator?

It could be a voltage spike causing the issue. What steps have you taken thus far?

yea i figured the problem would be related to that. havn't done anything about it yet since it doesn't seem to be serious. Not sure what to do about it though?

Problem something i could fix on my own ya think?

When just idling in gear at low speeds the car seems to jerk according the the jump in the tachometer.

If you have access to someone with the software to read out faults (if any) that would be the next step I would recommend. That same software would also be able to read live data stream which could also be very useful. If not then maybe there is something that is we can do, first do you have the radio code (if the stock radio is still there) if so, then try a battery disconnection for several hours (overnight) and see if it changes anything. This is similar to resetting (ctl,alt,del) your home computer.

i disconnected the battery over the weekend but the tachometer seems to still jump when i turn my highbeams on.

I am researching and will get back to this ASAP