1988 G20 running bad after tune up.
 

Last weekend I put new plugs and wires on my van and it runs worse now than it did before. Rough idle and sluggish. A few months back a put a new cap and rotor on it and those were Accel high performance. I also replaced a couple of rotten vacuum lines too. Since my cruise control is dead I got rid of the diaphragm and rolled up the vacuum line and harness. I plan on pulling plugs to check their gap. I'm stumped.

Did you correctly place the spark plug wires to the proper plugs, and follow the firing order on the distributor cap?

As far as I know I did. I did check to see if the old wires were ran the same as the diagram I downloaded before I took them off. I would think if I had even 2 wires in the wrong place it would be backfiring.

I'd strongly suggest you recheck the plug wires

So you're saying if 2 wires are on the wrong plug it will still run without back firing? As soon as the weather cools back down here I plan on taking the 4 plugs back out I just put in and rechecking the gap. I don't plan on driving it much until then. I'm going to look for the firing order on the manifold in the event that this isn't the original motor. I've looked online for spark plug wiring diagrams They all show the same thing.

When you changed the vacuum lines did you do the vacuum advance? Yours has a carb right?
Re check you plugs to be sure, and then make sure there is no shorting. ie they are routed properly.
You can use a plumbers torch to let a little propane out near the intake manifold and use it to look for vacuum leaks.....if the idle goes up, you have a leak.

I didn't see a hose for vacuum advance. No carb. It has TBI.

Vacuum is produced at the intake manifold, regardless of whether it has a carb or fuel injection.

Does putting a litte gas in the throttle body help or are we just talking spark and timing olnly? (could it be a fuel issue by some coincidence)

I don't think so. Back in January I replaced cap & rotor and all 4 spark plugs on the passenger side. It made a huge difference. A month ago I was digging through my tool chest and came across the other 4 new spark plugs so I went a nd bought new wires installed the 4 new plugs and all the new wires. Now it runs like crap. It's getting gas.