1999 Mazda B2500 (Ford Ranger) revs own engine

I've got an odd problem with my 1999 Mazda B2500 (Ford Ranger under the hood), I'll post as much information about it as I can and see if it makes sense in the end.
About two months ago, I had the following work done on the truck, in the following order, all within about a week of each other:
1.    General oil change/filter change/rotate tires at Jiffy Lube. Check all fluids, top off anything that needs it. 2.    Regular tune-up at the dealership (Carmax), including replacing the spark plugs (four cylinder engine), check all filters/belts/hoses, etc. They didn't bother checking the battery (you'll see why I mention that later). They "tweaked" (to use their words) the way the truck was idling in the computer settings. 3.    Two or three days later, the truck won't start. First person to look at it and jump it says my battery is dead. I drive to an auto parts store down the block, they check it and say it's not the battery but the alternator. I drive it to my mechanic, he pulls out the alternator, tests it, says it's charging fine, then tests my battery and says that's the real problem. He puts my original alternator in and a new battery.
After all this, things run fine for a couple of days. Then the problems start.
They can be best described as the engine running too high. When I turn it on first, it idles at about 1,200rpms for a few seconds, then drops to around 750rpms (what it should normally idle at). When I get on the road and start going, the engine problems come up. First, when put the clutch all the way in to shift up (or coast to a stop), the engine will either maintain its speed when I put the clutch in or actually increase speed (usually gradually over a few seconds, not a jump all at once). It will go well over 3,000rpms before I either turn the engine off or put the stick up into 5th gear and ease off the clutch a hair at a time to try to choke it off (depending on if I'm stopped dead in traffic or up-shifting on the road). I normally shift between 2,000 and 3,000rpms, depending on whether I need a lot of horsepower (like getting on a highway) or if it's cold outside and I'm trying not to push her too hard until she warms up.
This happens intermittently and randomly, both when the engine is cold and when it's hot from driving for hours non-stop. As I said, it happens when I push the clutch in to either shift or to come to a stop. It will occasionally do this also when stopped dead, not moving (just sitting idle).
I've also noticed that when driving down the road, the engine will occasionally maintain speed without giving it any gas. My clutch is rather old, so I can feel a jerk if I take my foot off the gas for a few seconds and then put it back in (even when I ease it in gently, you can still feel it "grab" when it first gets started). The vehicle does this occasionally on its own - I take my foot off the gas to cruise a little and after a few seconds I notice I'm maintaining speed, without touching the gas, and the cab will jerk a bit as if I had gunned the engine.
All of these things have occurred, obvious, when I wasn't touching the gas pedal. When I say it revs on its own, I mean it literally revs on its own. I've gotten interesting (dirty) looks from people crossing in cross-walks in front of me lately (to which they get the sheepish "It's her fault, not mine!" look).
I've been to three mechanics a total of four times, and so far I've been told there is nothing they can do since when they road test her, she doesn't do anything like I've described. I thought maybe it was my fault, even though I'm not driving her any differently. I've been very mindful of how I'm running her the last few days, and the problems are still there, whether I beat her hard down the road or treat her with kid-gloves.
As I said, it happens equally often (and randomly) when the engine is hot and cold, when it's been driven all day or left to sit all night and started in the morning cold. The only way to stop her is to either put it up into 5th gear (if I'm not there already) and ease the clutch off to choke her down a bit, cut the engine, or wait until she chokes herself out.
The only other odd thing she does (and this is something that's happened since I bought her a couple years ago from Carmax) is a valve on the driver's side under the hood (part of the exhaust system) makes a clank-clank-clank noise. The valve has been replaced and I was told that it's just a noisy valve and there is no problem with it. It has gotten much noisier since this all started, but I haven't had any idiot lights go off (like the last time the valve went bad, when my dash lit up like a Christmas tree). I've noticed that when the clank-clank-clank starts, the engine idles a little rough. I'm hoping (honestly) that this is related to that valve, and it will go bad again soon and set off my idiot lights, since without idiot lights nobody can/will fix her.
At this point, I've ruined the good relationships I've had with the only decent mechanics in my area (that I know about), all of them thinking I'm crazy since it won't do it when they drive her. I'm getting tired of hearing "Are you sure it's doing this?," or the more popular phrase, "Could it be operator error?" So far, they claim to have done the following:
Check all the hoses Check all the valves Check that all the fluids are topped off Check the sensors Check the cable on the cruise control (plenty of slack, not hanging) Connect to a computer to dump codes (there are none) Road test it (to the tune of about a tank of gas) Let it set idle all morning in the garage Hook a mobile computer up to monitor the computer while driving
As I said, they can't find a problem, though it's getting worse.
Any suggestions? I'd like to get some ideas of what it COULD be before I drive it to the Ford/Mazda dealership locally to have them take a look at it (my last desperate hope in having this fixed).
Anything you need me to clarify, let me know.
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The first thing that comes to my mind would be an IAC that intermittently sticks full open. As we drive, the PCM will open the IAC all the way so that it can use it for "dashpot" effect if the throttle is closed suddenly. While some state that they are satified with the results of cleaning these valves, I refuse to risk the reliability of my repair on cleaning and opt for replacement.
HTH
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I'm with Jim on this one. It sounds like you have a dirty/defective IAC. The fact that the Carmax techs "tweaked" the engine idle tells me that the IAC was not maintaining proper engine idle and that they have no idea WTH they are doing. There is only one idle adjustment there. It is not in the computer setting as these cannot be reset or changed w/o re-programming the ECM which only Ford dealers can usually do. The idle adjustment that is there is the base idle that must be setup "by the book" and is never used to adjust the idle speed if the IAC cannot handle it's job just because it needs to be service or cleaned. If I were you, I would find a tech that has some idea of how it works and get it corrected. The IAC needs to be properly cleaned or replaced. In the process, the throttle body should be cleaned. If the IAC cannot be cleaned to work properly, it should be replaced. You should also know that the IAC will not always set a fault code when it does not/cannot work because it needs cleaning. Have the MAF cleaned while they are at it.
BTW, your problem is not odd. The only thing "odd" about it is the fact that techs continued to screw around with adjustments before taking care of routine housekeeping chores. Profits are good on plugs, wires and filters but, not so good on routine cleanup chores. It takes time and most folks don't want to pay for house keeping work when it is "obvious" that it need new plugs and wires if it's been over 10 miles since they were last changed. Hell, the last guy probably didn't even know WTH he was doing!!!
Good luck Lugnut
On 2 Oct 2005 18:45:25 -0700, snipped-for-privacy@vcu.edu wrote:

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Could it be a sticking throttle cable? I don't know if that is something they checked. Mine certainly behaved exactly that way. When it 'revs' itself, try pulling up on the gas pedal with your hand or foot. If it revs down when you do that, it is almost certainly related to your throttle cable.
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