IACV hunting with ignition on, engine off.

[thompster]

Lots on the forum about hunting idle but I can't find exactly this.  When I turn my ignition on the IACV hunts constantly but the car starts and runs fine and the hunting stops once running.  Is this normal and if not what should I do?  EU3 K16 with Supersport ECU in case it matters.

[Ian Mackenzie]

I seem to remember mine doing the same when I had a k series, so from my perspective it sounds normal.

cheers Ian

[SM25T]

They all do that sir.

[thompster]

Thanks both..  its always done it a bit but tonight it seemed more frantic than normal. I'll stop worrying.

[john milner]

Mine (VVC) doesn't do any hunting. I thought hunting was a sign of a disconnected IACV. It may not make much difference at this time of year but in the winter there may be a starting problem so is worth delving into further.

[john milner]

http://www.tom-seven.stillgame.ch/wiki/doku.php?id=idle_air_control_valve

http://www.tom-seven.stillgame.ch/wiki/lib/exe/fetch.php?media=connector:iacv-logic.jpg

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

[Jonathan Kay]

What sound are you describing, please?

Thanks

Jonathan

[Smithy77]

From when I had a K with IACV, I remember the stepper motor chattering/hunting for a second or two after switching off, which is normal as I believe it is finding the starting position for next start up. I don't ever recall hearing anything before starting though....

I would look for a spare IACV and do a swap and see if it does the same. They are handy to keep as a spare

[john milner]

If mine chatters/hunts it is for less than a second as I have never noticed it. I thought it only had to find its position after a three press reset or battery disconnect and with a simple ignition off it should remember from last time.

thompster said "When I turn my ignition on the IACV hunts constantly" which does not sound right to me.

[revilla]

It's quite normal. The IACV is a stepper motor under the control of the ECU and there is no feedback so when you hear it moving, it is doing so entirely under the control of the ECU and not of its own volition. It certainly won't be a fault of the IACV itself as the ECU gets no information back from it (it's doesn't operate as a servo). As well as the extended chatter when shutting down (the ECU winds it closed by enough steps to ensure it is fully closed then back open to the correct position for the next start), if I turn my ignition on and don't start the engine, after a while it starts chattering again. Not sure why, I guess the ECU is responding to fluctuations in temperature readings etc. and trimming the start position accordingly. I really wouldn't worry.

[john milner]

Mine doesn't chatter. Should I be worried?

[revilla]

Naaaah! Just leave them to do their own thing. Only worry about fixing them of you actually have problems!

[thompster]

Some interesting posts there.  My IACV has always chattered a bit (learnt the correct term now) but usually settles down.  Yesterday I was fitting new wiper blades as part of my LM Classic prep and the IACV was chattering away non-stop.

I reseated the plug but no difference.  If, as said above, the IACV doesn't feed back to the ECU then the chattering has to be either because the ECU keeps changing its mind, or possibly because the IACV can't set itself as requested - maybe it keeps overshooting or is gummed up?  I guess that depends on how it actually works, what the ECU is acting on and whether the IACV knows if it's moved correctly.

Revilla - you're right; if it ain't broke and all that.  But I can't believe a K16 in a Rover 25 or MGF or whatever does this, and a few people above have said their caterhams don't so it does seem a bit odd.  Fingers crossed it goes back to a slight chatter and gets me to France and back but if anyone has any technical info about how it actually works and what the ECU does I'm all ears.

Edited:  John Milner - thanks for those links to detailed info.. just reading them now.

Double edit: From one of John's links:

S2 (PWM) The S2 ECU cant measure where the IACV is so has to count the drive pulses it sends and remember the position, 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.

So.. perhaps this explains why not everyone has this and why production rovers didn't: if you have a battery isolator it will hunt on start-up and if you don't it won't.

[john milner]

Is the chattering heard when sitting in the car with the bonnet on? I'm wondering if I have never heard it due to where I am when I turn the ignition switch. I hear the fuel pump but not much else.

I am on my second IACV the first started giving cold start problems which I managed to get a year or two extra life from by cleaning out. My existing IACV is intermittently starting to have the same problem but due to the warmer weather at most needs a few seconds of open throttle to work around. I'll give this one a clean out in the autumn.