S1 IACV?

[r10crw]

My new S1 has been running okay but when it first came home the idle would hunt occassionally. For example coming off throttle with clutch in the revs would rise and fall to a near stall before finding a reasonable idle just a bit lumpy.

The car has the standard inlet manifold but head has some work and cams so guess the idle was never going to be perfect.

Anyway cleaned the IACV and things improved but Ive noticed that between gear changes or on downblips the throttle doesnt fall as quickly as Id expect. Initially I thought airleak but all looks well at least from the IACV conenction.

Is this a common sympton of a faulty IACV, just replace?

[Ferg]

I had this recently and although my solution was to change the throttle body, common things to look for that cause this include sticky throttle linkage by the pedal box and melted throttle cable as it passes the manifold.

[Fluoxetine]

I'm sure you have, but did you do the IACV reset procedure when you plugged it back in?

[tut]

Also finding a difference with the new car Craig, clutch in to change gear and the revs are rising which they did not on N3, so have to make a slower gear change.

It has a lightened flywheel which I did not have, so would that account for it?

tut

[r10crw]

Thanks all,
So, Idle reset procedure ehh?? Who'd have thought....

Tut, you tried lifting earlier?

[tut]

yep, have started doing that now, but it is not instinctive and slows down the change, not important on the road, but a drawback on the track.

Check it out and see what I mean.

tut

[woody]

Idle reset? I know there's a reset for the throttle position.

[robin]

I think the MEMS learns IACV position dynamically; when you first turn the ignition on you should hear the MEMS rattle the IACV against the end stop - that's it zeroing the IACV, then it steps it forward to best guess as to required position based on coolant temp. Revs slow to fall are normally air leak into manifold (could be breathers, the inlet manifold gasket or the throttle body, or bad cable adjustment).

Kangaroo idle is normally the result of cams with too much overlap causing pulsing in the inlet manifold which in turns screws up the MEMS because it uses inlet manifold pressure and doesn't expect it to pulse. You can mitigate this a little by using a bore restrictor in the IACV air path - this will reduce the gain of the loop and make it more stable, maybe, maybe not. You could also consider backing off the overlap a little - depends on what cams and whether you're planning on revving the scunners out of it ...

Damping the vacuum hose to the MEMS also might work for similar reasons (low pass filter into the MEMS eliminates the pulsing) and normally should be OK because the MEMS detects transients using the TPS; the MAP is only there for steady running type stuff.

You can tell if you have significant vacuum leak; when the throttle is closed, clamping the IACV pipe should make it stall (you can also remove the IACV pipe and just put your thumb over the end. If it doesn't stall, air is getting in another way.


Tut, the revs climbing on lift off is due to the pressure reservoir effect of the intercooler, I think. I had the same thing on the 240 - I never proved it was that, but it seemed likely; you just have to adjust your driving style accordingly; lift off a few 100ms earlier; the engine will still push momentarily. Maybe worth asking the normal Honda gurus whether this is normal for the conversion and whether it can be tweaked to get rid of it.

Cheers,
Robin

[Fluoxetine]

Idle reset? I know there's a reset for the throttle position.

This is what I meant: http://wiki.seloc.org/a/Idle_Air_Control_Valve

Or for non-SELOC'ers

"Resetting" the iacv

S1 (Stepper) The IAC Valve postition maybe reset by switching the ignition on disabling the imobiliser and pressing the throttle fully and slowly 5 times, it may also be reset with the Lotus check tool. This is detailed in section EMN page 14 of the service manual.

S2 (PWM) The S2 ECU cant measure where the IACV is so has to count the drive pulses it sends and remember the poistion, then tries to return to a datum every ignition on/off. If it loses track e.g. battery disconnected the ignition needs to be switched on to position 2 and off several times to run the valve back to the datum.

[woody]

Idle reset? I know there's a reset for the throttle position.

This is what I meant: http://wiki.seloc.org/a/Idle_Air_Control_Valve

Or for non-SELOC'ers

"Resetting" the iacv

S1 (Stepper) The IAC Valve postition maybe reset by switching the ignition on disabling the imobiliser and pressing the throttle fully and slowly 5 times, it may also be reset with the Lotus check tool. This is detailed in section EMN page 14 of the service manual.

S2 (PWM) The S2 ECU cant measure where the IACV is so has to count the drive pulses it sends and remember the poistion, then tries to return to a datum every ignition on/off. If it loses track e.g. battery disconnected the ignition needs to be switched on to position 2 and off several times to run the valve back to the datum.

Pretty similar then, I'd been thinking of this:

http://wiki.seloc.org/a/Throttle_Position_Sensor

Manual recalibration

In all cases a manual recalibration of the TPS may resolve the issues at least on a temporary basis. To recalibrate the TPS: -
With the engine off, insert the key and turn the ignition to position 2 (On) without starting the engine.
For MEMS-equipped cars (S1)Or S2 Rover engined cars, quickly but steadily press and release the accelerator pedal 5 times for TPS calibration, using all of the throttle travel as practicable. It is better to do this from the engine bay, using the cam on the throttle body, as this ensures you get 0-100% operation of the throttle, and correct calibration, If your throttle cable or mech does not give 100% throttle, calibration will be out. And potentially you will be wasting your time. This will trigger the ECU into the closed-throttle reference learn algorithm, which has it looking for the lowest measured static throttle position (the closed position). The throttle position calibration is a fixed definition from this point.
Turn the ignition off, remove the key and wait for the ECU to power down (about 30-40s).
Start car as normal.