Help! 95 Rough Idle

[95pologreen]

My 95 vette has recently developed a rough idle it started about a month ago and has got worse. It has 115K on it. When I start it up it feels like its shaking, when I put it in gear thats when its felt the most. It has excellent acceleration with no problems. Its starts right up with a tap of the key. I noticed something strange last night about it. I put new spark plugs in it as the ones in it were the originals and they needed to be replaced. I took it out for a road test stopped at a store. When I started it back up it was shaking REALLY bad and I noticed the charging voltage was way low. I put it in drive it took off with no problem voltage went up to 13.5 and stayed there, it was like when I stepped on the gas pedal the charging system switched on. When I got it home I tried to recreate that problem but it started up fine and the voltage was good too. The Opti Spark and the water pump were replaced about a year ago. All of the old plugs were evenly burned and had no traces of coolant or oil. Any help will be greatly appreciated.

 

[toptechx6]

Assuming there are no fault codes in the PCM, it sounds like you have a cylinder misfiring. A couple of suggestions that may help would be to inspect the spark plug wires with the engine running at night or in a dark garage, any arcing of spark to ground indicates the wires should be replaced, don't forget the coil wire.
If the wires look good my next step would be to try to isolate the misfire to a specific cylinder, not difficult since your 95 has sequential fuel injection. With the fuel rail covers removed (just pull them straight up) and the engine idling unplug each injector one at a time. Idle quality should get worse if a cylinder is functioning properly when you disconnect the injector, if you find one that does not change the idle when you unplug the injector that is the offending cylinder.
Once you isolate the dead cylinder you will then need to determine the cause, make sure it is getting spark, ohm check the plug wire for continuity to the plug it could be broken internally even if there is no arcing observed as above, even with a good spark plug and wire there could be a problem with the distributor cap.
Next check to make sure the injector can deliver fuel to the cylinder, ohm check the injector it should read between 12 and 16 ohms but understand that only checks the injector coil electrically it could still be plugged and not flow fuel, check the injector wiring with a noid light to verify the PCM can operate the injector, if those tests pass you could swap the injector into another cylinder then recheck as above to see if the misfire moves with the swapped injector, not that difficult on an LT1. If the misfire follows the injector swap after checking out electrically the injector is likely plugged or not operating mechanically.
Once you verify spark and fuel delivery to the cylinder the last variable is mechanical condition of the cylinder, start with a simple compression test, then remove the valve cover to verify pushrod and rocker arm function, by that point you should know what is causing the issue.
The sequence above is not chiseled in stone and can be varied based on tools available and your ability, the important part is to systematically eliminate each variable in turn until you determine the root cause of the misfire, good luck.