s2000ellier

TB probably sticking, aftermarket TB are not the best

EffWun

Mine has gotten this issue too, another symptom is the revs will sometimes hang (no CDV on ap1 slave, aftermarket cmc replacement.) I eventually got a cel for TPS (Throttle Position Sensor.) The CEL went away within 30 minutes of appearing and never came back (Two months ago, but following symptoms still present.) Idle now actually can happen around 800-900 as normal but still have the 1.1-1.5k high idle pretty often in addition to the occasional rev hang, especially when cold driving.

TPS seems rather annoying to change and I am not bothered by this situation too much, doesn't seem to affect hard driving when fully warmed up.

aaronyuri

That would be the butterfly valve in the throttle body sticking during lift off, causing more air than expected to enter through the TB (beyond what the IACV can police with PWM control). Usually a clear sign of a poor quality TB...

Rather than the butterfly valve sealing and the idle passage allowing air in based on the idle adjustment screw position; air is passing the butterfly valve and increasing engine RPM. The IACV will reduce its PWM duty as low as the ECU will allow but too much air is still entering the TB.

I suspect you lift off, the revs are quite high, idle PWM duty drops, idle settles a little lower and then never drops beyond that position.

Solution: reinstall the OEM throttle body. Easy.

EffWun

Update for my fix (problems could differ per individual) - Eventually got a misfire and tps CEL. Changed coil packs and added fuel injector cleaner. Disconnected neg battery terminal for ECU reset and car is now back to normal. Idles between 800-1000 and drives smooth. Hopefully this helps somebody eventually.