IAC valve help!
 

Well I have been doing the Idle problem searching as many know but I have come to completely suspect the IAC.

When I have the car to the on position, not running, I can get 12 volts from the IAC terminal and a ground point and across the IAC clips terminals. However I can not get a continuity reading to ground with the car on.:wtf:

Heres the Question:

If I can get a 12 volt reading across the clip doesnt't that mean the ECU is getting a ground for the IAC? The ECU was replaced by a dealer for not having ground.

If the IAC clip is pulled the idle does not drop at all.
The IAC's resistance is within limits.

Well this is my last attempt to fix it before trading in the car for whatever I can get. So hopefully someone can hewlp me out!

what? again?

well the wires could be fubar too

The car has been to 2 dealers know with no fixes only BS!

The wires from the IAC to the PCM are good, verified numerous times.

To clarify:

There are only 2 problems that can be determined.
1) the car idles way low and the car will stall when returning to idle.
2)If the IAC valve's clip is pulled the idle has no change.

I was hoping someone may have an idea based on the Voltage test I did at the IAC harness and if not seing a ground on terminal B is normal.

Re: IAC valve help!
 

If you're using a multimeter, you will typically NOT be able to get a continuity reading with the car on. Continuity testers are meant to work when a circuit is NOT charged.

Yes, theoretically it does, but what you need to do is compare the 12V measurements- (1) across the IAC terminals and (2) from the IAC terminal directly to chassis ground. The terminal measurement should be lower, but not by more than ~0.5V. If the terminal-to-terminal voltage is too low, check continuity between the IAC terminals and the correct ECU plug pins with the car turned off; this will tell you if the problem is in the IAC-to-ECU wiring. If these wires have continuity, then the problem is within the ECU somewhere.

BTW have you tried replacing the IAC with a known good unit? Since you're reaching your wit's end, the dealer may be willing to try installing a new one to see if it fixes the idle problem.

Ain't electrical troubleshooting fun? :mad:

I have already verified continuity from the IAc clips wire to the ECU wires, with damn near no impedance drop at all. So i know thats cool.

I was hoping the dealer would replace the IAC first but they were convinced it was the ECU, which it appears it wasn't. At this point I am on very bad terms with 2 of the 4 dealers in my area, the 3rd i know to be useless and the other is an 1.5 hour drive. But none the less I will try again.

Trying to find someone with just a protege around here let alone willing to swap IACs for a few minutes is damn near impossible but If anyone is willing to lend me one I will make it worth there trouble, $$$$$.

Thanks again Bro, you have helped alot.
Is there any definite way to make sure the ECU is fine.

Doesn't the IAC operate as a servo, and a constant 12V indicate it's stuck and not responding? The resistence can be in spec and it still be stuck. I've seen this several times, and it can be a real bitch, especially when it blows the servo driver in the ECU. Sometimes a good cleaning and lube will fix it. But a new one isn't that much is it? Why won't the dealer install one?

The 12 volts was measured across the clip ot the valve itself.

You said if the valve sticks it can blow the serve driver in the ECU. How can this be determined and would it appear that the ECU is not giving the IAC valve ground if the servo driver blows. The dealer told me the IAC was getting no ground which is why they replaced the ECU but it sounds like the IAC can freeze up and smoke the ECU so I am in danger of it happening again!

DOes anyone know what cuases the seize?

As for the dealer not wanting to replace the IAC, I have no idea.
There is one other dealer I want to try before giving up all together. Maybe they will know a little more.

Zeus are you a Mazda tech?

I'm not a Mazda tech, and I don't even no if the IAC in the Pro is a servo, stepper or rachet type pindell. But I have had this problem with a civic and a GMC truck though. All the GM needed was a flush with carb cleaner and some WD40, it wouldn't idle at all.

The Honda's stuck at cold idle, which was about 1800 when hot. There was no hope for that valve, so I tweaked it to close it down some till I could get a new one. Problem was I didn't disconnect it, and by the time I got one the ECU was NFG. The tweaked IAC and ECU worked fine for many more miles, except on cold starts. I'll be damned if I was buying a $1200 ECU for a old Honda. I got a refund on return of the new valve to the dealer, so I got used to it.

That info is probably of no damn use to you at all. I just thought I'd share it. Be glad you didn't have to hear my EGR and smog pump stories.

When you say clip, do you mean the IAC connector looking back at the ECU? Because that's what I assumed. If there were no ground return through the ECU, you shouldn't be able to read 12v becasue it would be floating. Right? Also if it is a servo type, it could have a separatly derived voltage driver, with it's own return not referenced to chassis. That's why you don't read 12v to chassis.

My cheap advice would be to try removing it and adjusting it like it were a idle screw. If that works disconnect it until you can get enough info together to fix it right.

Anyway, good luck figuring it out.

Thanks again.
Yea clip meant the actual molded wire harness that ataches to the IAC vavle. I am not sure what it is but I know the old probes which had a smiliar valve loved to stick so I removed mine and cleaned it out. The only problem is it would seem that you would need to lube it up some how so it doesn't get stuck again but I didn't know what to use to do that or if I even should.