Wise guys. :D

So I checked the factory manual. I hadn't been able to find the right section before. But I found it. They list 26 separate things to check for a rough idle like mine. The O2 sensor is one of them. This could take a while.

By the way, is that engine fuel-injected, or carbureted? If the latter, maybe it's a jetting issue.

When we were on our last day of driving to Yellowstone, we were about 20 miles out in farmland when a loud hiss arose form the front of the car, Oh Crap!, is it overheating? gauge says not, just the AC wheezing ? then it dies away, weird we drive on.
About ten minutes later it starts again getting louder and softer, sounds right at the front, like it's coming out of the heating vents. After moving my hands around covering things up to see what changes the sound I notice the radio is on, but there are no stations out there it's just the static coming and going
:blush:

It is fuel injected.

So in addition to hooking it up to a code reader, the shop manual says to:
- check oxygen sensor
- check throttle position sensor
- check engine coolant temperature sensor
- check MAP sensor
- check if problem occurs when engine is running Rich or Lean (I think it's lean when it's hot, which it is)
- check evaporative emission (EVAP) control system
- check fuel injectors
- check fuel pressure
- check ignition voltage output
- check spark plugs
- check spark plug cables
- check ignition timing
- check for vacuum leaks
- check the ECM/PCM grounds
- check ECM/PCM for A/C signal
- check EGR
- check battery cables
- check A/C refrigerant pressure
- check PCV valve
- check for broken engine mounts
- check valve timing
- check low compression
- check bent push rods
- check worn rocker arms
- check valve springs
- check camshaft lobes

Holy crap. I can rule out about half this stuff, because it doesn't make the metal clanking sound of worn valves or bent push rods or anything like that. And it has nothing to do with the A/C being turned on. And we just replaced the PCV valve. The spark plugs and distributor cap are not as new as I thought they were (they are about 30K miles old,) but the cables look good and clean on the outside.

Many of those items need not be checked either because they should never fail in the life of the car, or would be obvious from sound and observation.

Never need replacement include spark plugs and wires, rotor and cap, and PCV valve.

Would be obvious for other reasons include: fuel pressure, fuel injectors, battery cables, broken engine mount, and valve timing and those other related entries including camshaft lobes.

These entries should result in a check engine code: oxygen sensor, throttle position, coolant temperature sensor, MAP, most injector problems and low fuel pump pressure, EVAP problem (that will even detect a missing gas cap), ignition timing, and EGR.

I have no idea why refrigerant pressure is on the list unless they are discussing a mechanic who over pressurized the system.

That should seriously shorten a list of top suspects. Having said that, I don't know how 'good' your car's diagnostic software is. But being 1996 or later means a diagnosis is much easier due to that computer diagnostic port.

Have you ever read "Shop class as Soul craft" tw? You might benefit from it. It's about an ivy league college graduate (probably an mba to boot) who's taken up motorcycle repair. He finds a sublime pleasure in diagnosing the trouble in a poorly running machine, kind of like glatt's situation.

I ask if you've read it because there's a thought expressed in the book I think you'd appreciate. The author says that there's an absoluteness to the machine. That despite the theoretical, the documented, the machine doesn't really care. That it is up to the mechanic to observe, to listen to what the machine is telling him, and then respond accordingly, even if it is contrary to "the book".

When you say things like "spark plugs and wires and caps and rotors never need replacement" I just roll my eyes. I don't know anybody who has any actual wrench time that would say such a thing. No one who has spent time actually working on cars would ever entertain such a ridiculous notion in a situation like this. Maybe, maybe in a theoretical discussion of what a perfect world would be like, etc. But come on. That's not what glatt's dealing with. His car's running roughly in some conditions and it is completely reasonable to think that a misfiring cylinder because of a bad spark plug could cause this, as an example.

If you're just ranting, rant on brother. But you're not giving much practical help here with proclamations like that.

My main point is when you say "should never fail" I have to edit it to read "probably isn't the cause of your problem, but ...". It irritates me.

My wife reports that it's not doing the rough idle today. A couple days ago she filled the tank with the super premium gas because she had an 80cents off code from the grocery store. Hmm. Don't know if those two facts are related. I need to continue the observations.

So stop reading so much theory. Learn from those who were edcuatd by reality. So many cars (even in the 1960s) were fixed by learning this stuff the hard way. In the 1960s (due to bad designs), spark plugs and wires had to be replaced constantly. When one who mocks your theoretically trained author, instead, designed an installed an electronic ignition in a 1960s car, then spark plugs never needed changing. How many engine systems did your guru design? How often did he also trace failures back to the source by learning from the hardware?

So many religiously trained mechanics preach, "But the car has a heart". Many are recommending tune ups and wheel alignment only because it increases their income. All cars (even GM) no longer have nor need tune ups. But then I a stating this because I not only know this stuff by doing it. But also designed parts or traced failures to defective designs.

Any car that needs spark plugs, wires, or cap in 200,000 miles was probably something designed by a bean counter in GM. Even GMs parts can not longer fail as frequently as they once did only due to Federal laws.

Listed where the more likely suspects. Only those being scammed by a mechanic need replace spark plugs, wires, or cap even in 100,000 miles. What was once required every 5000 miles or three months was obsoleted decades ago when EPA rules made current technology required in all cars.

TW, I think you need to read Big V's post again.

It may well be that spark plugs should never need replacing, that's the theory. Each car is it's own independent reality, and we've got to allow for the fact that quality control was pared back by MBA managers to save money, and that the car was built and serviced by humans. You know, those frail, irrational bags of mostly water?

It's like with the paperless office discussion. You're not allowing sufficiently for human fallibility.

Human? What's that?

Last time I looked, Limbaugh was being sponsored by spark plug companies. Sandusky recently said to take a defensive position. Replug annually to avoid infant mortality.

The scheduled maintenance for this car makes no mention of changing the spark plugs, but for cars that routinely tow, it says you should change the plugs every 30k miles.

I had read several years ago that plugs today are really good, and that you could go 100k miles on them (or more) but they get to be very difficult to remove if you wait that long to switch them out, so consider switching them out sooner than that.

Did the outside temp change? My money is on the O2 sensor.

We should all bet on it, and whoever is right gets to pay for the repairs.