Now that I have an automatic trans in place, I need to get the idle a little bit better under control. Things seemed to work pretty well until mid summer last year, and then got a little shaky. It would idle about 300 RPM too fast from time to time, and then settle back down. That was OK with the stick shift, but the auto requires a more stable set up. Here are a few questions:

1. Anybody cleaned the GM style IAC valve? I think this one is hanging up once in awhile. Do you just pull it out and clean it out with brake or carb cleaner?

2. I have never understood how to calibrate this valve and the Mega Squirt software that goes with it. I have read the manual several times, but it just does not click yet with my poor old brain. Any advice on this would be appreciated.

3. Before I put the auto in it would start, and then idle high for about 10 seconds, ad then come down, just like OEM EFI setups. The feature seems to have disappeared. I did not intentionally change anything with the EFI hardware or software. Do you think the auto trans puts enough drag on the engine that the idle is held down? The engine does idle considerably smoother with the auto trans than it did with the stick, which suggests that the auto acts as a pretty major damper/flywheel kind of calming influence on the engine.

Sam

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My thinking is a little clearer on this now. I found lots of information on line about cleaning the assembly. Confusion is around setting the base line for the pintle distance from the mounting surface. Most say set it to be 28mm (just over an inch) out. But then some say simply push on it to set it where it belongs, and others say DONT push on it. You might damage it.

Then there is the Mega Squirt settings. This was done originally by Peter in Virginia Beach, and I do not know what he did. It never seems to have worked the way it is supposed to work, but worked well enough to keep it from dying when cold. This engine runs so well now that it will start and idle at 650 RPM when dead cold at 35 degrees outside temperature. Sometimes I think I should just disable the IAC. Thoughts?

Sam

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Cleaning did not help. Matt is trying to tutor me through this now. It is above my head for sure. Plus the weather has not made it easy to put in time on it. I spent the morning shoveling 17" of snow from around my daily drivers.

I cleaned the servo, and that did no good. It was not very dirty. I did determine that the valve is not closing all the way, and it idles too fast even with the throttle adjustment all the way down. Next is the check the circuit itself, and then try and run the built in diagnostic in tuner studio. I am hopin it is something as simple as a bad wire, and not a blown component in the ECU. I am wondering if there is a stand-alone IAC module. There is no reason this has to be integrated into the ECU. All it would need is the temp feeback from the sensor in the head, and a simple tuning program to adjust the amount the servo opens at various temps.

Sam

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When you say "GM style" IAC, is it a 4wire unit with a sort-of conical tip? That type is a "stepper motor" servo- it has 2 electromagnet coils inside. The pcm will alternate power to each coil, which turns a magnet a little bit each pulse. The magnet has inside threads (like a nut)- that screws or unscrews the pintle (which has alignment slot on the shaft so it can't spin) & the conical end of the pintle blocks off as much of the air bypass port as needed. The pcm reverses coil polarity to go the other way.

I would wonder if there is a way to test the pcm's ability to properly drive the IAC? I would also take a really good look the wiring diagram to se if the IAC is wired correctly- it will act really weird if 2 wires are swapped "across" the 2 coils.

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63 Valiant Wagon
225 - 4 bbl

It worked OK for almost 3 years. There is a test for the IAC. I am just beginning to wrap my mind around it. It first involves a VOM check to see if the circuit will carry current. Then it involves turning the key on and off looking retraction for in the pintle. Then there is another lap top test to see if it will extend. I think I am going to need another set of eyes to do the second and third test. For now I have blocked it off.

BTW, it is a 4 wire valve with a square connector.

Sam

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If it moves at all in both directions its likely not a hardware issue. Sam, get a longer usb cable and run it out the window. They make wireless (bluetooth) adapters you can use but its more costly and hassle then need be for this exercise. Put your laptop on the fender or one of those foldout tv tray tables. Then you can man handle the motor and laptop at same time.

These little things have incredible torque. In my electronic geekery, I made a device that can drive these motors forward and reverse with the touch of a button. I can send it to you so you can test your IAC separate from the MS if it comes down to it.

I would like to make a separate driver just like you made. I would just use it manually like an old model T throttle control on the dash. Can you either supply me the circuit, or make one for me for a fee?

Sam

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Sam it involves a custom programmed chip (micro controller) - giving you the schematic won't help unless I program a chip and send it to you. I've long since lost the original program. Shouldn't be hard to recreate but will take time. This wasn't ever meant to stay in car, just for testing. I suppose it should be used as a manual idle speed control though.

We can arrange for something but I think your best plan of (long term) action is to get the MS under control.

Some IACs are hard to test because they need engine vacuum to actually move......

Just listen for the solenoid clicking when adding and removing power.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

This isn't a solenoid - this is a 4 wire stepper motor driven directly from the MS - no relay/solenoid. It's functional regardless of vacuum.

You could google for Thexton 398 IAC tester - it pops up now & again on ebay. It has clips that hook to the car's battery & a couple connectors that plug into different styles of GM IAC motors. You push either button to command the IAC open or closed. (still got mine in my toolbox at work- used it last month on a 83 Camaro)

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63 Valiant Wagon

225 - 4 bbl