Will not idle/stalls

We need to know the idle steps the computer is setting the AIS motor to, and whether the actual engine speed is responding appropriately.

The next thing is to look at the sensors to see if one's signal is changing significantly when the erratic idle speed or rough running occurs. When we find a signal voltage that is bouncing around, we have to determine if the signal is wrong and the computer is commanding a response that is creating the running problem, or if a sensor is seeing the incorrect engine operation, then the sensor is reacting to that. Mainly it is the front oxygen sensor that sees a change in mixture and reports that, but it gets confusing because the computer reacts to those signal changes by commanding another change in mixture.

The scanner also counts misfire events. Most of those are too subtle for you to feel, but when you observe rough running, it will be bad enough to show up on the "misfire counter" display. If that is listed as a specific single-cylinder misfire, you can switch the injector, ignition coil, or spark plug with those from a different cylinder, then wait to see if the misfire switches to one of those other cylinders. When it is listed as a "random cylinder misfire", they're all being affected by something they have in common. You'd go looking for things like low fuel pressure, a vacuum leak, a stretched timing chain on engines that use them, and things like that. A stretched timing chain is just one thing that can slap against the housing, then, if a knock sensor is used, it will pick that up as spark knock, and the computer will retard spark timing. When that gets bad enough, it can feel like a misfire, but the computer will know it is adjusting timing, so misfires aren't really occurring. There won't be any misfire fault codes even though that's what it feels like is occurring.

Basically you're flying blind without a scanner. When I whine and snivel that there's too many computer controls for things that don't need a computer, (like heater controls and interior lights), I'm always told those computers make diagnostics so much easier, ... If you have a scanner. Trouble is, we wouldn't have so many breakdowns if there wasn't so much electronics involved. Dust, moisture, heat, and vibration are the deadly enemies of electronic circuitry, so the insane engineers can't seem to add enough, whether we want it or not.

The point I'm trying to make is there is no way to know where to start looking without a scanner. You must have data or diagnostic fault codes to provide a place to start. Even when there is a part referenced in a fault code, that doesn't mean that part is bad. In the case of an AIS motor fault, those are so tough inside, you have a 95 percent chance of finding that code is caused by wiring or connector terminal problems.

I don't know anything about jet engines, but I'd be willing to bet you didn't try to solve problems by throwing random parts at it. There has to be a reason to suspect a part before you order a new one. Car engines aren't quite so serious when they don't run right, but each time you replace a part, especially sensors, you add a new variable. The computer has to relearn the characteristics of every new sensor. When it has no way of knowing you put a new one in, ... Take that MAP sensor, for example, it has the learned personality of the old one in memory. No two sensors ever develop exactly the same signal voltages under the same conditions, so if the new sensor's signal voltage is different by.02 volts, the computer interprets that the way it did from the old sensor. .02 volts makes a big difference with a MAP sensor. It will learn the new sensor's characteristics when a specific set of conditions is met, but one of those conditions is typically that no fault codes can be set for anything else it uses for reference, or for any operating conditions it watches to see how those change when it makes changes. An example of that would be when it opens the purge valve to draw gas fumes out of the charcoal canister, it expects that extra fuel to make the front oxygen sensor's readings go more rich. If it has already detected a problem with the oxygen sensor's circuit, it knows it can't use that for reference, so it will not set a fault code for, "insufficient flow" from the purge valve.

Most of these '96 and newer computers can detect well over 2,000 defects, and while there can be a dozen fault codes it can set related to just one sensor, they mean very different things.

One thing I used to read about fairly often related to erratic idle speed was most people found a small vacuum leak. I have never run into this myself, but leakage past the throttle blade shaft was common. You might try spraying that with water or Carburetor Cleaner to see if it has an affect. Also look at the gasket for the throttled body assembly. Those used to shrink on the Horizons and Omnis, then the carburetors would be loose and vibrating, and of course they didn't run well.

I understand completely. I'm in a different situation. My friend has a Snapon scanner that I can use, but he's 30 miles away. I do building construction and woodworking projects as a hobby, I was a tv / vcr repairman for over 35 years, and I was a mechanic for 16 overlapping years. For all of those, I like having the tools to make the jobs easier or faster, and I don't have family distractions to dictate where I spend my bucks. As such, I have much better and more tv repair tools than my boss had at the tv shop. I've been buying saws and routers if I think I can use them a second time, and I bought the same model Snapon scanner my friend has just so I don't have to run to his shop. Often that hassle isn't worth the time or gas to run there. My relatives are amazed at the tools and equipment I have amassed, and they know they can borrow stuff any time.

At the dealership, I had the biggest tool box, and I never locked it. Coworkers knew they could borrow a tool once in a while. Salespeople knew where to find a screwdriver at night if they needed to transfer license plates. I even had my own scanner there so I never had to wait in line to use the shop's.

We had a lot of repeat and regular customers who I got to know, and many of them were do-it-yourselfers. It was common for us to borrow tools and service manuals to them. The service advisors even had the dealership owners' blessings to photocopy pages out of service manuals, when they weren't busy with other customers, and they were to locate and borrow service manuals to the other new-car dealers in the area. We often shared manuals, information, and special tools, and at times we would repair each other's trade-ins.

My reason for sharing all of this is in every one of my careers, we built a network of resources and people to look to for help. If any mechanic tells you he is an expert in every specialty, look for someone else to fix your car. Those days are long gone. We have to specialize in a few areas, and enlist the help of others when it is warranted, just like doctors do.

Start with a mechanic or shop that has a good reputation, and explain the problem you're having with no scanner. The worst they can do is say they don't borrow tools. Shops with less than stellar reputations will usually not be very busy, and they will want to keep all repairs to themselves. The good shops have plenty of work waiting, and they might be happy to help guide you, which they might see as easing their backlog. They appreciate good word-of-mouth advertising, so it's in their best interest to try to help you. They are likely to not want to let you take their scanner, but they might allow you to use it in their parking lot.

Another good resource is the people who drive the tool trucks around town. They typically visit the same shops at the same time and day each week. Any mechanic can tell you the names of the salespeople and when they show up at their shop. Snapon, MAC, Matco, and Cornwell are the common ones. They also have the "used drawer", as I called it, where you can check out the tools that were traded in. Where this can help you is at times they will have a sale for a new scanner pending until the buyer can sell his old one. That old scanner isn't on the truck, so no one else is aware it is available unless they ask and are specifically looking for one. This happens with tool boxes too when the mechanic is trying to sell it to a new mechanic and when he thinks what he was offered for trade-in isn't enough. The salesman will usually direct you to the person who has the used scanner for sale, and he doesn't ask for a commission, because he's going to complete the sale of his new one.

I just looked at the DRB3s for sale and was shocked to see what they're going for. One guy wants $199.99 for a replacement cable! I bought three new spares a few years ago for ten bucks each. Considering these scanners last worked on 2008 Jeeps, they're going for way too much money. The better alternative now would be the Snapon Solus Edge. The one I bought is updated through 2018 models, but because those annual updates are so expensive, these scanners lose their value very quickly when they are out of date. If you find one of these updated to only 2014, the four updates at $1000.00 each would cost more than buying a new scanner with the latest updates. This is where it is an advantage for people like you. You can find these out-of-date scanners for less than $800.00, and there's a good chance you can use it for a few years, then resell it for just as much as you paid for it. You can learn to use a simple code reader by reading one paragraph. The training manual to learn everything the DRB3 can do is over 1/2" thick. Once you play with one, you'll never want to be without it again.

For my last thought of great value, consider looking for a nearby community college with an Automotive program. We were always looking for live work to give the kids real-world experience. Be aware though, they will only take in cars with engine performance problems when they are teaching Engine Performance. For us, that was only once per year, for eight weeks. They won't look at yours when they're teaching Brakes class, for example because that would take away from their instruction time, which is already too short, and it would take potential work away from the local employers who hire their graduates. It can take a while to get the car back, but cost of parts is about the same as what you'd pay at the parts stores, and labor charges are real low. Some schools also offer night classes for people in the community. We used to have two open shop classes, each running one night per week, when you could do anything you were qualified to do, and an instructor was there to offer advice. Here you would have access to a number of different scanners, and a pile of resource material.