The two pictures are from my Blazer (yes, I know, wrong plugs). I was able to work a bit this evening on my truck (idle tweaking) and thought I'd replace the Autolites with AC Delco Iridium plugs (41-993).

When I took out the old ones, the plugs for cylinder's 1,3 & 5 looked a bit dark in color and I could smell gas from the plug holes. The spark plugs from 2, 4 & 6 look okay to me.

Do you guys think this could be a "spider" issue? If so, this might explain my slightly rough idle problems.

 

One side is running rich or has oil contamination.
Now why... spider - possibly but for only the ones on 1 side, that's odd.
Same with manifold gasket or valve seals.
It seems like only 2 of them are darkened, might still be manifold if they're ajoining cylinders.

This is by no means a remidy or a proper way for things but... the 2 that are dark, open the gap of the plugs .005 & see if that helps. They'll burn hotter & may not cause the stumbling.
Have you checked the gaps of all the plugs you removed to make sure they have the same gap?
Check the O2 sensors on the Y pipe, if one is messed up it'll cause the PCM to run rich or lean.

 

I replaced the down stream O2 sensor about two weeks ago but I haven't changed out the other two sensors. In fact, they maybe original sensors

I was able to replace the plugs pictured with AC Delco Iridium's last night. This helped a lot but then again, the gap measured a bit larger than the Autolites.

I've got a little time today to mess around with it some, so, I'll look into regapping the new spark plugs first. Hopefully this will help out some more or at least until next payday.

 

Update:

So, I was able to re gap the #3 & #5 cylinder plugs to something around .065 (my wire gauge only measures in .010 increments) and drove about 25 miles. Here is a picture of the new plugs.

Number 3 doesn't look bad but number 5 is really black. No oil this time. And, just like the last time, I got a strong gas smell as soon as I removed spark plug #5.

So, all others being relatively equal, I'm starting to think I need to either clean the injectors or save my pennies for a new "spider" assembly.

 

How are the wires, rotor & cap? Maybe there's an issue with #5 not getting enough spark?!

 

The distributor cap and rotor are one week old (AC Delco brand). The wires, who knows? I think those are next on my list of replacement parts. I was thinking it could be the wires because of how old they look and how easy it is to remove them from the terminals. LOL

Oh, I need to replace the distributor as well. This afternoon I noticed one of the screw bosses for the cap was broken off. The cap isn't loose, thank goodness, but the boss literally crumbled in my hand! LOL

 

Another update:

I got to thinking about this problem and thought I'd do a little more digging and came up with this picture.

According to the EDI timing DIY write-up, the rotor in my distributor is off several degrees. And, the distributor itself looks to be off several degrees. I say this because the front flat section of the distributor is not parallel with the front of the engine.

Yes, I understand the PCM controls timing but I think at some point, someone either replaced the distributor or moved it without checking crankshaft and camshaft alignment.

Am I right about the distributor and rotor alignment? Or, am I not seeing something.

Oh, and what size wrench do I need to use to unbolt the distributor?

 

The downstream O2 sensor monitors the efficiency of the catalytic converter, that's all it does, it has nothing to do with vehicle performance. The PCM uses data from the upstream sensors to adjust fuel mixture.

A bad O2 sensor on one bank will affect the fuel mixture on all 3 plugs on that bank... probably not a sensor causing just 2 of them to foul out. Could be plug wires, or possibly a leaky injector, or poppet valve if the injector assembly has not been upgraded. A fuel pressure leakdown test would find that, but the fuel pump must be isolated from the injectors, and the return line corked off just after pressurizing the system.

Make sure the new plugs have a gap of .060"

Good quality plug wires are usually good for 100K miles. If yours are original with 171K miles, they are well overdue for replacement. Autolite Professional Series wires have better specs than AC Delco, and at 1/3 the price, it's a no brainer

Distributor:
If DTC P1345 is not in memory, and the SES light is off, the distributor gear is properly meshed with the cam gear. Whenever the distributor is removed, camshaft retard should be checked and adjusted if necessary. It's done with a capable scan tool, (not all of them will access it). If/when you replace the distributor, get one with an all aluminum housing, not plastic like the original one. The distributor hold down bolt: If you use a 10mm, 1/4" drive swivel socket, a 6" extension, and a ratchet, you can get right on it, piece of cake:

 

The only code in memory is a P0300. This showed up later this evening when I was test driving the truck around the neighborhood. I also noticed, at the same time the code was thrown, how rough the engine pulls between 1200 and about 1800 rpm. This may have been there before this evening but it was the first time I noticed it.

I also tested for a leak in the plug wires this evening with a little help from a spray bottle. Nothing. I didn't see or hear an arcing sound anywhere in the engine compartment; however, not knowing the age of the wires, it might be best to replace them anyway.

 

Now the pro is in, that means I'm out. At least I had a good thought with the wires, was a little off with the O2 sensors, but in the same ball park. & the distributor does have to be put back in the same way (aligned) as the old one came out.