Ok, here's the deal... I'll try to keep it short.
99 Altima, 5 speed, 116,000 km.The idle speed was a little too high when I got the car, but by adjusting the idle screw (all the way) I got it down to around 750 RPM.
The problem that I'm still having is, as I ease into the throttle, as I cross around 1250 RPM, the revs will suddenly increase to about 2,000 RPM even though I haven't opened the throttle any further. This manifests itself as an abruptness when I ease into the throttle while on the road, or when I take my foot off the gas.
If I disconnect the IAC valve, this doesn't happen.
In looking at the factory service manual, I see that the IACV should be at around 20% at idle, and they show just a dash ( - ) at 2,000 RPM, which I assume means 0%. They also show a scope reading, which appears to show the IACV pulse being on for 4ms and off for 2ms at idle, vs on for 2ms and off for 4ms at 2,000 RPM.
If I'm reading that correctly, then it would appear something's causing my IACV to stay open MORE at 2,000 RPM (or above 1250 RPM).
Any thoughts on this? Everything shown in the manual as being used by the ECU to determine IACV position as far as I know is OK with the exception of the ambient temp switch, which I haven't tested.
I'm totally confused as to why the IACV would open further as I'm opening the throttle, unless it's programmed that way to help keep the revs up while taking off from a stop with the clutch, but I would expect they would cancel this behavior once the car was moving more than say 5 km/hr.