My check engine light is on

[Cloud]

I'm sure they'd be willing to refund me the $500 + for the actual part . . . if they removed it and put my old PCM in there (if they even still have it). Don't really want that, though, nor do I want to make a big scene. I received the same diagnosis and suggest for a fix from two different places, and went with that, but I knew there was a chance that it wouldn't fix the problem. I will keep trying--have to, anyway, since it's my only transportation option.

I really appreciate everyone's advice. The Cellar is really great for that! I refuse to be ashamed that I'm not good at fixing cars. I'm not an idiot, but I'm not handy, either. I try to keep my car well-maintained anyway.

In the end, I listen to advice and use my own common sense.

[tw]

Originally Posted by Cloud

I received the same diagnosis and suggest for a fix from two different places, and went with that, but I knew there was a chance that it wouldn't fix the problem.

They simply followed a simplistic diagnostic chart. It says if the valve clicks when voltage is applied, then replace the computer.

Well, an idle air control valve actually opens and closes quickly per commands from the computer. So quickly as to need an oscilloscope to actually see it. Computer monitors how fast the valve is responding. If the response is not what was ordered, then the computer flags a check engine code. If the valve works normally but too slow, then computer gets replaced (if only following the diagnostic chart). Valve can be sticky, partially clogged, etc. and still pass the on-off test.

The entire circuit is real simple. Computer tells valve to open and close rapidly. Valve opens and closes rapidly. If valve does not do that fast enough, then an error code is created. Only three things in that circuit - computer, wire, and valve.

How I would have responded? I would have asked why they knew the computer was defective. I never mention the IACV. Let them mention the valve and why they know the $200 valve is not defective. I have found only some mechanics who really know their stuff because the word why is used heavily. The stuff I do not know then gets confirmed later with an internet search.

If anyone tells me something without the reasons why and without numbers, then he is lying.

Standing in the dealer to get a new oil filter or wiper blades is very educational. Watching them talk to women quickly separates honest dealers from the shady ones. Numbers (verses no numbers) quickly identifies the honest ones.

[xoxoxoBruce]

Sure, they went through the diagnostic procedure, and when some part that is acting up intermittently, worked at the time, they blamed the PCM.

[tw]

Originally Posted by xoxoxoBruce

Sure, they went through the diagnostic procedure, ...

Diagnostic procedure does not work for intermittent problems. It can only identify a constantly defective part. Intermittents require additional facts.

In a previous discussion, I noted Toyota's biggest problem. People. In this case, the mechanic cannot really be effective if, for example, the exact conditions during every 'failure' are not defined. For example, Cloud later noted that this failure occurred as the car was warming. Also critical are factors such as where the temperature needle on the gauge was located during each failure? Was it accelerating or during constant speed? How many minutes after starting the cold engine? How much gas in the tank? Was air conditioner on? Headlights? Does it happen at night and day? Does it happen when going uphill or down?

Just a short list of what must be provided so that a mechanic can really do his job. A problem because most people cannot bother to collect facts or make the problem reproducible. And because so many people only get angry when asked question after question. So many want intermittent problems solved immediately.

So a mechanic (if not provided an oscilloscope and without information on how to make the problem reproducible) can only keep replacing parts until something works - shotgunning. That will be the solution here.

Check list said if the IACV is not constantly failed, then replace the computer. Check list procedure does not address an IACV failure that occurs, for example, only as the engine gets warm. Only way a mechanic can find / fix that problem is if a person / driver volunteers that fact.