My '95 Rodeo has 113,000 miles on it. Its last tune-up was 6 years ago at 77,000 miles (plugs, timing, fuel filter, "fuel induction service", various things checked.) I think it needs another one because I'm noticing a slightly rough idle and a drop in fuel economy from 16-19 mpg to 14-17 mpg. The air filter is fairly new and clean. Some questions:
Which spark plugs should I use? Does it matter that I live in a hot climate (Phoenix)?
Should I replace the fuel filter again?
What else should I have done in the "tune-up" category? (I'm pretty good about other maintenance such as engine oil & filters, transmission oil & filters, differential and transfer case oil, etc.)
The work will probably be done at a nearby Firestone Auto Center because there's a nice sports bar next door to wait in. Are there any special instructions I should give them?

I'm not sure why timing is mentioned since it not adjustable. Pretty much the only thing to getting a tune-up is new plugs and maybe wires. Other than that, there is no tuning involved.

When we do a tune-up it includes, plugs, wires, cap & rotor,( if applicable), Air & fuel filter, & compression test. The compression test is performed first to detect any cylinders that have less than 100 psi. This will cause a miss and rough idle. A tune-up will not cure low compression.

All tune-up parts that are ordered are required to be OE or equivalant.

Hope this helps

Fuel filter and plugs could definitely need to be changed out.

2.5yrs ago my truck was also experiencing rough idle, feeling like it was missing too, turned out my waterpump and timing belt tensioner were failing, causing the belt to loosen.

Runs like a charm now...need to do my plugs and filter here soon too.

I'm not sure why timing is mentioned since it not adjustable. Pretty much the only thing to getting a tune-up is new plugs and maybe wires. Other than that, there is no tuning involved.

I mentioned timing in my post because it says "checked timing" on my receipt for the work done 6 years ago.

With respect to the wires, those were replaced in that same time period with the "new type" that prevents oil from leaking past the boot (or something like that.)

As a follow-up to my original post:

The Owner's Manual gives the following spark plug specification:
FR2LS/BKR6E-11/K20PR-U11 gapped to 1.05mm (.04 in.)
I presume these are AC Delco, NGK and Denso part #s, respectively. Over and over I read posts that say these engines are very sensitive to the spark plugs. Which ones do you guys recommend? How about traditional type vs. double platinum?

Tune-up to me would mean:

1. Check and replace plugs.
2. Check and replace air filter, PCV, and crankcase filter (if applicable).
3. Check and replace cap, rotor, plug wires (if applicable).
4. Check timing and adjust (if applicable).
5. Check accessory belts and change if needed (PS, AC, etc).

Other items fall into routine maintenance (oil filter + change, transmission filter + fluid, coolant flush, etc).

Periodic maintenance would be shocks, timing belt, brakes, etc.

Oh, and in both Isuzus I have owned the standard copper core NKGs work(ed) the best. The Bosch +4s got all fouled up in my Isuzu pickup and the platinum plugs in the Passport sucked until I replaced them with the el cheapo NGKs.

Over and over I read posts that say these engines are very sensitive to the spark plugs. Which ones do you guys recommend? How about traditional type vs. double platinum?

Its only on the '00+ rodeos that you need to worry about specific plugs because they have ion sensing ignition system which use the plugs as sensors. '99 and older arent picky about what you use. I prefer denso because they've always worked best for me. I refuse to use champion or bosch, they never lasted more then a couple months for me. I run double platinums because they last much longer. Tune ups lost their appeal for me.

Sounds like you're due for the timing belt/water pump deal. I might suggest front O2 sensor replacement at that mileage, especially since you are noticing a drop in mileage.

Sounds like you're due for the timing belt/water pump deal. I might suggest front O2 sensor replacement at that mileage, especially since you are noticing a drop in mileage.

The timing belt, tensioners and water pump were replaced at 83,000 miles. If an O2 sensor was bad, wouldn't that trigger a check engine light? Also, wouldn't that cause the Rodeo to fail its emissions test? (I'll find out in 3 months.)

If an O2 sensor was bad, wouldn't that trigger a check engine light? Also, wouldn't that cause the Rodeo to fail its emissions test? (I'll find out in 3 months.)
Not always. They get weak over time and can send a low signal the ECU but not low enough to trigger the CEL. It will cause the ECU to think the engine is running leaner then it really is.