Re-built Bosch alternators... idle fix

[Dustn525]

My friend's ETA had an an idle problem, until now. He had bought a rebuilt Bosch alternator. Bosch is a high-end, OE supplier. However, their re-manufactured alternators come with the casings re-painted. As well as no pulley. No biggy, until the paint.

You will find that there are 3 power connections, and the smallest of the 3, grounds <some shit to do with> the idle control valve and whatever else. It grounds to the casing, which was painted over...

His car ran like a douchetard, until we got it back here and sanded down the grounding point to bare metal, then re-attached the small ground wire. Car runs smooth as ever now. :) The ICV was not receiving proper voltage signals because it wasn't grounded properly, as other sensors probably weren't either.

This is something that no-one ever checks, so do it if you're having problems. The airbox is easy to remove, and underneath you will find the alternator -- it's easy to access on both "e" an "i" motors.

[Bryan///]

Great advice. Thanks for lookin out

[chance]

my 91 318I idles like shit, and I bought it with a new looking alternator. I will check this

[5Toes]

Hmm will try!

[stamar]

I wish.

mine is temperature sending unit.

[thebutterson]

I had a similar problem with a generic replacement alternator, except I had to add a ground wire to the body of the car. Otherwise when I turned the key the battery light would come on automatically. The troubleshooting section of the bentley led me to that idea.

[Gregs///M]

Mnn, that is strange. The schematic for the alternator does not show any wires going to the ICV.

Red - to starter (12V charge)
Blue - Cluster and ABS unit (excitation circuit)
Ground is through casing. Perhaps your casing mounting points had paint on them? Did you add any additional grounds?

Also the ICV schematic has three wires.

Two go to the ECM for motor control
One goes to power.
None directly to alternator.

[b*saint]

Its the grounding of the sensors apparently ground to the alternator. I wouldn't imagine they would be directly connected.

[Gregs///M]

No, all engine electronics are grounded through the Engine to Chassis ground cable. From oil pan to frame rail on drivers side.

[b*saint]

That's what I would figure also. I think that the casing is ground to the chassis for electrical noise, I don't think it has to do with the sensor's path to ground.

If you alternator was putting out a shitload of electrical noise, then it could induce incorrect voltages in surrounding sensors.