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<< adjusting the idle screw with the IAC in place seems useless >>
Is your idle-bypass screw (the black one) tightened all the way in ? I suspect it is, given your throttle-butterfly valve is not completeley seated like mine. In any case, you should be able to at least RAISE your idle with that screw by unscrewing it.
<< This isn't what I was expecting. I was hoping to hear the armature clicking stop to stop. >>
I too had expected that. Actually the 2 transistors controlling each of it’s 2 coils are able to keep it in one of countless positions between closed and fully-open.
<< I believe that maybe one coil is fully grounded and the other is being pulsed with a varying duty cycle which presents an opposing magnetic force of a variable magnitude >>
I don’t think it works this way. If it did, the maximum it could be controlled was from fully-closed (if the closing-coil was grounded) to half-way closed.
<< I am not a big fan of piercing insulation of wires >>
You don’t need to pierce wires. The way I check continuity is by either...
- probling the inside of the component-connectors after peeling back the rubber boot
- disconnecting the large grey connectors in the passenger-side of the engine, and probing the inside of them
and the best way...
- disconnecting the large ECU connector, loosening the single screw on it that allows you to open out the connector exposing the back of the terminals along with the pin-numbers – and then checking continuity to the TPS, IAC etc. This allows you to check whether the TPS is functioning (by opening and closing the throttle), check coil-resistance of the IAS, Temperature sensor etc. You also end up verifying that your wiring-harness is fine. And most important, you verify all of this as close to the ECU as you can get.
<< I suspect that if the ecu must see "idle on" if it is going to close the IAC for base idle adjustment >>
Not true. When I had the IAC rigged up so it was being run by the ECU but didn’t have rubber hoses attached, it didn’t swing closed if I opened the throttle. Even with throttle opened a lot, it took a while to creep into the closed position. And remember – it never really fully-closes in base-idle.
<< In the throttle body, I too can see a halo of light around the throttle plate when fully closed (stop screw fully retracted). Is this normal? >>
No – this is not normal. I ended up compensating for this by fully closing the idle-bypass screw. However, one thing you should note is that even with the throttle-stop screw fully removed, the butterfly-valve could still be held from fully closing by the stop in the TPS switch. That’s why it’s important when setting the idle-stop on the throttle-body to loosen the idle-stop screw, loosen the TPS (or better still – remove it) and THEN set the idle-stop screw. You then reconnect the TPS switch and adjust it’s position. You might find you don’t have a halo any longer.
Noel
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