Originally Posted by LATECH
On a TBI engine there is no advance mechanism. Its all calculated by the PCM
You can add more timing to the base or inital timing to compensate for things like cam duration.Put a vacuum gauge on a manifold source to help you get it to a happy spot between Idle qaulity and speed.
Base timing , and computed timing are basically stored in the PCM algorythms. It does have an "Adaptive strategy" which will allow the timing to run further advanced if it detects octane will support it, and retaard the timing when the low octane fuel causes a knock or pre ignition, which is detected by the knock sensor.
Its a good thing to have the kock sensor hooked up and working. As you drive the vehicle , the PCM will advance the timing through all the rpm ranges, untill it gets to the point it detects a knock, or pre ignition, at which point it will retard the timing until it stops.After that, and a few drive cycles, the adaptive part of the pcm will run the timing based on strategy it has developed through it range of operation.
The amount of timing that the pcm is delivering is based on the initial or base timing being correct.Or factory spec as on the underhood sticker.
If you add some base timing, you will have to add the extra amount to the value of timing advance that you see being displayed on the scanner.
OK. I'm getting the point here, I think. So I can adjust the initial time to fix the idle by advancing it. No worries about any other issue because the ecm will compensate. As long as my engine starts just fine, no hang ups, then I am good. That's assuming I have no piston ping...