Well, that was "Interesting"...
I disconnected the Idle Air Control to see what would happen on a cold start.
As expected, it took some feathering of the throttle to keep it running -- but after it warmed-up, it still required the input.
Some notable notations:
- High Idle disappears (good)
- (All the following items occurs, including after warmup...)
- When slowing to a stop, the car stalls in Drive before stopping (it's a nice smooth shutdown -- you don't even know it until the charge light comes on and the steering gets stiff)
- Vehicle stalls in Neutral (easy engine cut -- just shift to "N")
- Engine Code Thrown - P1503 IACV Malfunction
- Unknown operation: closed or open loop (used datalogger instead of SG-II)
Side note: the A/T version of this vehicle has a "Fast Idle Thermo Valve", which is a coolant operated wax plunger that keeps the idle up when cold (downstream of the IACV). This might be the target device, but has no "quick disconnect" -- it would require looping the coolant line back into itself (and no easy way to switch it).
Operation: What's fun, is that you can coast down at 400 RPM and keep an eye on things to keep from stalling, while in Drive -- and just give it a little throttle and off you go, or downshift to keep the engine alive...
To continue with this experiment, a couple things need confirmed:
- Is the low RPM operation potentially reducing the amount of oil and/or transmission fluid being pumped (down to a dangerous level)? It doesn't lug (so no concern there).
- I have a switch that I can wire into the sensor, so I could have more control when the vehicle is warm. Not being well-versed with feathering the throttle, some hard transmission engagements occurred at lights.
- Is this saving fuel, or could the ECU be compensating for the error? The
SG can answer that soon...
I have the shop manual which noted the IACV circuit is involved in a complex feedback system that's fed to the ECU and determines idle among a bunch of other things. It didn't go into detail on the specifics of the ECU's logarithms in this case, but instead circuit and device troubleshooting, so
Any thoughts?
RH77