1990 Chevy s10 blazer 4.3L V6 4x4 TBI

Voltage spikes to a lower voltage and almost dies when the ac/radio is turned on. Then, usually at a stop light, I will have the same issue sporadically even when no accessories are on. Major Tuneup was just done on it, cap, rotors, wires, fuel pump/regulator/filter, distributor, plugs, ecm, throttle body. Alternator, O2 sensor, EGR, and battery have been changed before bringing it in and it is still in the shop due to it being more than just idle issues that I originally brought it in for and the starter died while at the shop and it was changed. I have invested a lot in tracing the problems with this rig so I thought I would run it past the forum and see what you all thought it could be.

 

im either thinking bad ground. try doing the big 3 upgrade im thinking theres current being drawn else where or u have a short.

 

My thought was bad ground, or short. Big 3 is easy to do, and relatively cheap compared to other fixes. It won't help if it's a short, but should see an improvement in idle voltage if it is a bad ground. My buddy's 91 pick up had this issue and turned out to be a bad battery ground.

 

I replaced the big three and was still having the issue, the mechanic said it is the low idle causing the voltage spike not the voltage spike causing the low idle, so I am not sure what it is now.