Well, like it says, the truck has a rough idle that seems worse after long highway drives. By rough idle, I mean that it "shudders." It also will start shaking when under load in OD. Runs great through the RPMs though.
The plugs, cap, and rotor have 30k miles. Pulled a couple plugs (Bosch single platinums) and they look clean, maybe a bit hot, but still good. The wires are MOPAR and have unknown miles on them, but they are flexible and not damaged.
There are 50K miles on a Bosch O2 sensor.

Generally rough conditions are caused by a misfire, but being a college student, I don't want to just throw money at it. Any ideas on narrowing it down?

 

Have you fixed your plenum yet? Any oil consumption?

Check the cap and rotor. Getting to be about time for them to be changed.

Check the plugs in 7 and 8. Are they oil fouled at all? (ash deposits.)

 

so hot plugs look like they are brand new out of the box "white" color ( not golden brownish as they should) ?

 

I pulled #7. The plugs are halfway golden but have a small amount of white deposits.
The plenum gasket was replaced by a shop by the previous owner (keeping the steel pan), but the truck doesn't use any oil and the plugs aren't carboned up, so I figure that it's alright.
Unfortunately, since it's an OBDI, the computer is pretty useless for diagnosis.

Check the cap and rotor? If I check it, I'm changing it. What a pain in the ***. The last time I did it, I didn't get the rotor on quite right (I can't get a visual in any way, did the whole thing totally by feel) and shredded it, meaning that I needed to redo it. I question the necessity of having it in the seventh level of hell.

I guess it can either be a fuel, spark, or timing issue. The timing I can't control. The fuel would be affected by various sensors or a clogged injector. Spark would be everything from coil to plug.

 

On a side note, my parents 92 Plymouth Sundance can easily have all wires, plugs, cap, and rotor changed in under 10 minutes, if you're quick, under 5.

 

Since it's a '94 I gotta ask: Has the oxygen sensor ever been replaced?

If not, do it just because it needs doing. Also do it if it's been over 80k miles since it was replaced just because it needs doing. If it was replaced with something other than an NTK part, replace it because it's a chunk of crap right out of the box. Always use NTK oxygen sensors or those bought from the dealership, always always always.

The symptoms you describe are consistent with an early end-of-life oxygen sensor failure. A crank position sensor might do it, but that's a much longer shot. Heck, a marginal throttle position sensor might do it, but that's even longer a shot. So do the oxygen sensor if it's never been replaced or was replaced with something other than an NTK because it's can't hurt/might help.

 

Yeah, I probably should. It was replaced about 50k miles ago with a Bosch (by the previous owner). He said that it made the truck run differently than with the original sensor.
Any reason why NTK?

 

NTK or OEM are the best quality. More money yes, but worth it. I screwed around with Bosch O2 sensors on my 01 for a while till I installed and NTK pre-cat. Idle problem solved. Also do a search for the TSB on "Crossfire" I don't recall it it effected earlier 2nd Gens. But rerouting the wires may help some of the idle issue as well.

 

The NTK is the same price as Bosch and BorgWarner (BWD) and Denso. All right around $50 at NAPA (less at RockAuto). The BWD has a lifetime warranty though.