See "2.6 I-TEC, Really low idle" for some good pics of potential problem areas. If it's the 4ze you've got, my experience is you'll need to clean-up as much as tune up

Remove and clean back of throttle body
Remove and clean EGR valve and all associate passages
Remove and clean the pipe and orifice that feeds the bottom of the
back pressure transducer.
Give each vacuum port in the common chamber a blast of carb/throttle body cleaner.
Adjust your valves
Replace the PCV valve
Check all vacuum hoses for fatigue/cracks
Check belts. Replace belts if they look even a little cracked or glazed (something I failed to do in the past much to my chagrin)
Check air filter, replace if needed
Replace gas filter (I do it once a year)

Plugs? I stick with NGK. Gap is fine right out of the box.

A truck this old has lot's o' carbon especially if it hasn't been tuned right and most of it collects in the throttle chamber and EGR ports. If they are not clean it will not run right. One other possibility is someone messed with the throttle position sensor. Try this thread- http://www.4x4wire.com/forums/showf...mp;amp;o=&fpart=all&vc=1
Lots of helpful dialogue.

Thanks for the info. I am planning to overhaul the whole engine within the next few months.

Update:
In the middle of a rebuild, we found that the head gasket was bad between cylinders 3 and 4. The IAC valve is stuck open partially. Also, the explosions within the cylinders 3 and 4 have cut a groove into the head between them. This is what caused the head gasket to go. Also, the piston rings are bad on it which may have caused the bad compression. The valves are fine and in good condition. Thanks to everyone for their input!

Nope, the gasket went first then the gasses from 3 and 4 cut the groove.

Actually, the head probably warped due to over heating, causing the gasket to go and without the gasket, you ended up with the compression problem.

I suggest you look very carefully at the valves (or have someone do it for you). They are notorious for burning on these engines because people don't adjust them. As they wear into the head, they get tighter and tighter and finally they don't seal right and the valve gets toasted.

Good Luck,
Michael

I did. The valves are in great shape. The reason the rings are bad is that their are vertical lines on the cylinder walls and the walls are smooth as a babies bottom.

As in that is how I know the rings are bad.

Actually, it looks like someone put a new gasket on without fixing this problem first. I agree that the head gasket went first at one time, but it obviously wasn't this gasket. The groove in here looks like it has been there for a while since it is very deep.

I doubt it. You would be amazed how short of time it takes for super heated gasses to cut though Al. I promise you, it is not a defect that could be covered up, even for a short time, with a new gasket. The process is more like a blow torch, not erosion like water over a rock.

As for the rings, well...vertical marks in an 20-some year old engine, is not uncommon. If you can't catch your finger nail in them, they are probably not significant. How muhc of ridge is there at the top of the bore? These bottom ends are pretty bomb proof. If the rings were that bad, it would have been smoking like a freight train.

If you shine a light in there, I bet you can still see the cross-hatch pattern, despite the vertical marks.

Good luck,
Michael

There is an image of it.
As for the valves, I took them out today and they are in perfect condition. Just a little carbon on them, that's all.

Just took out the pistons today. Whoever rebuilt this engine last placed the piston ring openings on the same side near each other. Also, the rod bearings are wiped. The crank is in good shape other than some old oil. This engine has been neglected, and I am the one putting new life into it. I am having the block hot tanked soon.