Unable to diagnose

[crubio]

Hello everyone. I have a most unusual problem with my 1976 530i; I hope that someone has run into this situation before.

Most of the time, the car will start normally. By that I mean that the starter motor will spin quickly, and the engine will start. While I am cranking, the tach needle stays at 0 until the engine fires, then it goes to 1000 rpm.

Occasionally, the starter motor will turn much slower, and the tach needle will jump between 0 and 5000 rpm while I am cranking. Eventually, the cart starts.

I have a new battery, new starter, new alternator, new battery cables, cap, rotor, plugs and ignition wires.

Since the car does this occasionally, it is difficult to diagnose. Any thoughts might be appreciated. I checked my relays and cleaned the contacts. Could the combo relay be going bad, so the starter does not get all 12v from time to time.?

Thank you in advance, Carlos Rubio

[Mike W.]

If the starter is turning slower, start with the basics. Remove, clean and replace the battery cable connections at the battery, starter and ground. I don't care if they look nice and clean, you can't see resistance, remove, clean and replace.

[crubio]

That was my first thought. Every connection has been cleaned, but the intermittent problem still persists. Thank you.