I have had an 85 iroc 305 tpi for probably 5 years now. Really never has ran "well". Car has always had problems with this and that. You name it, it has probably been replaced motor and electrical wise. The car now acts like it has an electrical short. Car runs really rough when it is idling. When it is above about 900 rpm it smooths out. During idle it is running around 500 rpms, the oil pressure drops down and the volt gauge goes to about 10 volts. Also when I turn the turn signal on, the volt gauge bounces up in down in sequence with the turn signal. I put a heated O2 sensor on it and when the car is cruising, the voltage going to the sensor is zero. There are some times when I am driving the car the radio just turns off. The car almost sounds like it is not getting enough juice. I just replaced the alternator and wire going to it, and no change happened.

 

A few first things.

1. Have you checked / replaced the bigger battery cables?
2. Have you verified that the ground strap is in place at the back of the passenger head to the firewall?
3. Have you verified what the battery voltage actually is at idle and revving? You need a voltmeter for this directly on the battery terminals.
4. Have you checked for vacuum leaks?

 

I did end up replacing all the cable going to the battery. Ground strap from the firewall is in good shape. Also replaced all the vacuum lines with new ones. Still nothing changed. I will check the actual battery voltage when the car is running