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I have a 1994 base corvette that has a weird problem i can’t figure out the voltage tends to fluctuate a good bit sometimes dropping enough to stall out the car while i’m driving it’ll run rough a bit and stumble at times i’ve noticed the SYS comes up on my dash it also loves to overheat at idle but is ok while driving as long as i don’t stop wondering if anyone can give me some ideas on what’s wrong are these issues all related? is it maybe separate issues? here’s what’s all new on the car ( battery , alternator, all fuses, optispark, spark plugs, fuel filter )
The first issue could be your battery clamps aren't tight or you have a bad ground. Overheating could be a few reasons such as fans not coming on or dirty/clogged radiator fins.
Look at one problem at a time. I would start with electrical. Your overheating could be caused by low voltage at the cooling fan. You said you replaced the alternator. Did you replace that because of this problem? Parts store alternators have a very bad reputation for having problems out of the box. I always get one from a store that offers easy returns just for this reason. In my area Auto Zone is about the best for this.
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As already mentioned I thoroughly check the battery connections and grounds. Although new I d check the battery itself. Id also check the connections to the alternator.