Probably a Simple Electrical Problem

I suspect my 1989 325i has a bad battery, I'll get it checked tomorrow. However this e30 acts unusual compared to most cars with a bad battery. It turns over slowly (very slowly at first) and then fires up. It's a pretty rocky start and if left to idle it will idle at a bumpy 750 rpm. Also, the anti-lock light comes on. This past week I had my intake manifold off and repaired some vacuum leaks. I also had a coolant flush and replaced a couple bad hoses. I wouldn't think these things would be related, but is there a possibility they are? Tomorrow I'll be checking the battery, and looking around for any possible voltage draws when the car is off. Also, if that doesn't solve it I'll check out the alternator.

Has anybody experienced this peculiar low voltage/bumpy idle issue? Any recommendations for when I'm inspecting the electrical system tomorrow?

Check the alternator first. You can check voltage output at the battery with the engine running. Should be ~14 volts.

you could be getting a weak cell. do the test horn say, and if you have the good output get the battery load tested

+1 on both above. A bad cell/battery will drag the voltage way way down.

Any ideas on the random anti-brake light?

Low/weak battery will trigger all sorts of weird stuff.

Originally Posted by hornhospital

Low/weak battery will trigger all sorts of weird stuff.

Haha good to know, because there is a lot of weird stuff going on.

What about the idle sensor switch, located on the throttle assembly?

Sure enough, it was just a bad battery. That was probably the strangest bad battery I've seen.

you want my duc? i deal with that and worse anytime i fire the thing up when its under 50. normally the check engine and fuel light will come on and sometimes i get a coil message.

This morning was another bumpy start. Even with the new battery in there was still a stutter start and three check lights came on: park-brake, brake-fluid, and battery. These lights flickered off when I revved the engine and began driving. Do new car batteries need some time to be broken in or what?

Well never mind. The all mighty Google answered most of my questions. However I still don't understand why it wouldn't just be the battery light.

Flickering is either a ground problem or the alternator is getting flaky. Start at the battery ground cable and remove and clean every connection point. BMWs are probably the most finicky vehicles on the planet when it comes to ground connections.